I bought a roll of film to take pictures.

我买了一卷胶卷来拍照。

We hand in a roll of film, it gets developed, and we choose one photo for the competition.

我们交上一卷胶卷，冲洗后，我们选择一张照片参加比赛。

Where can I buy a roll of film?

在哪能买到胶卷？

A foreigner wants to develop a roll of film.

外国友人想冲洗胶卷。