He smiled suddenly, ____ (露出) a set of amazingly white teeth.

阅读短文，在横线上写出孩子们毛衣的颜色。

    Kate, Jim, Rose and Bill put their sweaters on the table. The sweaters are white，blue, red and black. We know the boys' sweaters aren't red and the girls' sweaters aren't black. What color is Kate's sweater? I don't know. But I know it is not blue.  Bill says, “My sweater is white”. Do you know what colors their sweaters are?

关于生态系统中各成分功能的阐述，正确的是（    ）