题干
—Many students are unhealthy because of a lack of exercise
—I agree. They should start exercising it's too late.
A：before
B：until
C：since
D：after
答案(点此获取答案解析）
A
＝a1a4－a2a3.将函数f(x)＝
的图象向左平移
个单位，以下是所得函数图象的一个对称中心是 ( )．