I was walking down the street when a UFO landed down.

问题描述:

I was walking down the street when a UFO landed down.
还有一个句子是When I went into the living room, I found Jack watching TV.
为什么第一个句子是landed down. 而第二个是watching TV.
当我进卧室我看到的不应该是一瞬间的啊.为什么用doing形式呢?

认真看,
found sb doing sth是固定用法,但是谓语是find,不是watching.这个find是短暂的,但是别人看电视时正在持续进行的.