当

当

"当" means "to be", "act as", "appropriate", or "at that time," depending on context.

In '当医生', '当' means 'to become', indicating a desire to assume the role or position of a doctor.

他小时候想当医生。

He wanted to become a doctor when he was a child.

In '当老师讲课的时候', '当' denotes 'when', marking a certain time frame related to the teacher lecturing.

当老师讲课的时候，我们要认真听。

When the teacher is giving a lecture, we should listen carefully.

In '当场的主持人', '当场' uses '当' as part of an idiom meaning 'on the spot', describing a location contextually.

他被选为当场的主持人。

He was chosen as the on-site host.