When you stop and think about your high school or college alma mater, were your experiences more positive or negative Do your feelings of (1) in that school have anything to do with whether or not your school was single-sex or coed (2) to send their children to single-sex schools, because they feel both (3) when they study in the company of students of the same sex. They (4) .
For years, only parents who could afford to send their children to private schools, or who had (5) , chose single-sex education for their children. Single-sex schooling was (6) for most American families. Today, however, along with (7) , public schools are experimenting with the idea of (8) .
Girls may be the ones who benefit most from single-sex schooling. Studies have shown that (9) in coed classrooms because teachers sometimes pay more attention to boys. Girls’ (10) toward their studies tends to disappear as they begin to feel less successful. They start to (11) outperform them in math and science. As boys (12) , girls start to lose it. Moreover, adolescence is (13) for girls. As they experience adolescent changes, some girls become depressed, develop an addiction, or suffer from (14) .
In the early 1990s, some influential people said that being in single-sex classes could (15) . Schools across the country began creating single-sex classrooms and schools. But many critics claim that (16) may actually be detrimental to a girl’s education because they (17) of sex differences.
The renewed interest in single-sex schooling (18) among Americans. Those who give it full endorsement believe girls need an all-female environment to take risks and find their own voices. Those who (19) of single-sex schooling wonder whether students’ lack of achievement warrants returning to an educational system that divides the sexes. They believe there is no (20) .

在空中某一位置，以大小v₀的速度水平抛出一质量为m的物体，经时间t物体下落一段距离后，其速度大小仍为v₀，但方向与初速度相反，如图所示，则下列说法中错误的是(不考虑空气阻力) （   ）

A．风力对物体做功为零

B．风力对物体做负功

C．物体机械能减少mg²t²／2

D．物体的速度变化为2v₀