题干
— It's the best time _____ in summer.
— You're right. But don't go _____ alone.
A：to swim; to swim
B：swimming; swimming
C：swimming; to swim
D：to swim; swimming
答案(点此获取答案解析）
D
内的图象是（ ）
，那么f（a）+f（c）﹣f（b）的值为（ ）