35-37 Have you ever heard of butterfly migration? They travel from one place to another during the year. One of the best-known examples is the Monarch butterfly migration.They can’t survive during the cold winters in the north and the center of the United States, so they fly south and west each autumn because it is warm all year around there. However, their overwintering places are under threat because the trees they could rest in are cut down for more space to build roads, houses, and farms. Look at the chart and answer the following questions.

migration遷徙survive存活 overwintering過冬的 threat威脅chart圖表
【題組】35. Which year did the number of Monarch butterflies drop sharply? & sharply激烈地
(A) 2011.　
(B) 2012.　
(C) 2013.　
(D) 2014.