1.去掉a,Martin is fifteen.
3.seem 接不定式：He doesn't seem to be happy.
4.trouble有时可数,有时不可数.
作具体的某件麻烦事情时是可数,例子：I find getting up early a great trouble.我觉得早起床可不容易.
作一般的麻烦,困难时是不可数.
When he was young,he often got into trouble with the police
5.give up 后加动名词：The doctor advised my father to give up smoking.