[Passage: The Mongol Army Takes a Rain Check] [1] In the summer of 1242, on the brink of conquering the Kingdom of Hungary in Central Europe, the powerful Mongol military suddenly retreated to Russia. [2] The motive for this strange withdrawal is not explained in written records, but some historians have asserted that it resulted from instability in Mongol politics. [3] Other scholars claim that the invaders simply decided that a full conquest would not be worth the trouble. [4] A recent study of tree ring data from Eastern and Central Europe by researchers Ulf Buntgen and Nicola Di Cosmo presents a compelling case that modest yet powerful changes in weather patterns played an essential role in this historic event. The writer wants to add the following sentence to the paragraph: "While these explanations may hold some truth, one factor likely played a larger role in the Mongol retreat than has previously been recognized: the weather."

[Passage: The Mongol Army Takes a Rain Check] From 1238 to 1241, which includes the year of the invasion and the years leading up to it, the region saw ___above-average temperatures___ and decreased precipitation. [See graph: Summer Temperature Anomalies from Long-Term Average Based on Tree Ring Analysis]

[Passage: The Mongol Army Takes a Rain Check] ___Before 1237,___ for instance, summer temperatures were about 0.5 degree above average. However, in 1242, the year of the withdrawal, this trend reversed, with precipitation increasing and temperatures dropping to as low as approximately 0.2 degree below average. [See graph: Summer Temperature Anomalies from Long-Term Average Based on Tree Ring Analysis]

[Passage: Evanescent Art] Many of the world's most famous works of art, such as Leonardo da Vinci's Mona Lisa and Johannes Vermeer's Girl with a Pearl Earring, ___were created centuries ago and are esteemed for their timeless appeal.___ However, not all art is meant to last.

[Passage: Evanescent Art] Over course of several weeks, the apple, which started out fresh and shiny green, gradually shriveled up before it eventually was replaced by a new apple and the process repeated itself. ___This new apple would likewise remain on display until it had fully decomposed.___ As Ono described the work...

[Passage: Evanescent Art] [1] Like Ono, Brazilian sculptor Nele Azevedo has experimented with transient materials to achieve her aesthetic goals. [2] Azevedo's work Minimum Monument, which began in 2005, involves her traveling to cities around the world, such as Birmingham, United Kingdom, and Lima, Peru, and, aided by locals, placing hundreds of tiny human ice sculptures at historical landmarks. [3] They evoke the forgotten lives and history behind the cultural monuments, and, as the artist reflects, their temporary life span helps communicate this message: "In the place of the hero, the anonym; in the place of the solidity of the stone, the ephemeral process of the ice; in the place of the monument scale, the minimum scale of the perishable bodies." The writer wants to add the following sentence to this paragraph: "These ice sculptures are left to melt and are meant to contrast with the permanence of the monuments on which they are placed."

[Passage: Evanescent Art] As Ono's and Azevedo's pieces indicate, ___works of art are subject to actual physical processes. Those processes can be key to their impact.___ Despite their apparent evanescent nature, these works of art convey substantial ideas...

[Passage: Evanescent Art] Despite their apparent evanescent nature, these works of art convey substantial ideas that artists and art lovers alike have grappled with throughout history and that ___will persist as those same individuals continue to seek out new ways to experience art.___

[Passage: Rubin and Ford Discover Dark Matter] The telescope-mounted spectrograph gave her a chance to pursue ___the interest that she had in galaxies. Then, she and Ford put the tool to use in studying___ the outer areas of galaxies.

[Passage: Rubin and Ford Discover Dark Matter] [Previous paragraph discusses expectation that outer stars move slower.] ___Eventually, Rubin and Ford would expand their research to more galaxies.___ They observed that stars maintained stable orbits of about the same speed no matter how close they were to the center of the galaxy.

[Passage: Rubin and Ford Discover Dark Matter] Rubin and Ford saw no such matter, but they were aware of theories proposing the existence of matter that could not be seen because it was nonluminous. ___After considering and excluding other possible explanations for what they had observed,___ Rubin and Ford hypothesized that they had found new evidence of the existence of this matter, known as dark matter.

[Passage: Rubin and Ford Discover Dark Matter] Rubin and Ford published their findings in 1970. Their work was initially met with skepticism but is regarded today as a landmark contribution to astronomy... At this point, the writer is considering adding the following sentence: "The work appeared in a journal that was founded in 1895 by two American astronomers."

[Passage: The Sweet Smell of Success] [1] "Fragrance is present in every aspect of our lives," says Rocio Arellano, a director of fragrance development at consumer product company Colgate-Palmolive. [2] From the aromas that lure us into stores to the smells that reward our housecleaning efforts, fragrances affect our perceptions and behaviors. [3] In fact, the marketing plan for Gain laundry detergent relies almost exclusively on the appeal of the product's variety of fragrances--including such proprietary scents as "Apple Mango Tango"--to ensure successful advertising results. [4] These scents are the creation of fragrance chemists, professionals who develop fragrances for consumer goods such as cleaning products, cosmetics, and air fresheners. The writer wants to add the following sentence to the paragraph: "Businesses know and use this to sell their products."

[Passage: The Sweet Smell of Success] ...use advanced laboratory tools such as gas chromatographers that separate and analyze fragrance components. ___Those studying to be fragrance chemists must also acquire the ability to communicate with nonscientists.___

[Passage: The Sweet Smell of Success] ...in-house chemists examine it and perform consumer ___testing. The chemists perform this testing in order to have the ability to make a decision regarding___ whether it works for the product being developed.

[Passage: The Sweet Smell of Success] Fragrance chemists are often expected to develop new fragrances that evoke particular emotions, such as feelings of happiness or nostalgia, but research has shown that various markets respond differently to the same scent. For instance ___in the United Kingdom, many people find the smell of baby powder easier to identify than the smell of lemon.___