现在进行时：
肯定句：He's climbing a tree.
疑问句：Is he climbing a tree?
否定句：He isn't climbing a tree.
一般过去时：
肯定句：He climbed a tree.
疑问句：Did he climb a tree?
否定句：He didn't climb a tree.
将来时：
肯定句：He's going to climb a tree.
疑问句：Is he going to climb a tree?
否定句：He isn't going to climb a tree.
现在完成时：
肯定句：He's climbed a tree.
疑问句：Has he climbed a tree?
否定句：He hasn't climbed a tree.