Jane's collecting shells on the beach.

简在海边收集贝壳。

How long has she been collecting shells?

她已经收集贝壳多长时间了？

Howlong have you been collecting shells?

你收集贝壳多长时间了？

A boy and a girl are collecting shells.

一个男孩和一个女孩正在收集贝壳。

He has been collecting shells for ten years.

他收集贝壳十年了。