Whichone is the topic sentence?（1）The 19th-century American philosopher Henry David Thoreau was famous for saying, “Simplify, simplify.” （2）Unfortunately, the trend these days seems to be “complicate, complicate” instead. （3）Many people are working longer hours, spending more money, and getting in more debt than ever before. （4）They are also relaxing less and spending less time with family and friends. However, there is also a countertrend―a trend toward voluntary simplicity.（5）People in the voluntary simplicity movement take various steps to make their lives both simpler and more enjoyable. （6）Some people work few hours each week. （7）Some move close to their workplace to avoid a long daily commute; they walk or ride a bike, instead. （8）Some plant a vegetable garden; this gives them fresh air, exercise, and time with their families—not to mention organic produce. （9）But all people in the voluntary simplicity movement try to cut back— to buy less; they cut up their credit cards and stop buying unnecessary items. （10） In short, the priority in the voluntary movement is to follow Thoreau’s suggestion: simplify.

A. 1
B. 3
C. 5
D. 7
E. 9
F. 10