请问:how could they have grown up healthily?是现在完成时吗?为什么不将have提

请问:how could they have grown up healthily?是现在完成时吗?为什么不将have提 Given more attention,the trees could have grown better.中为什么不 how long have you had to wait?had 如果是现在完成时,wait为什么不加ed, 请问,现在完成时比如说have kept 和have been done.那如果是have eaten中间为什么不加be ___more attention,the tree could have grown have grown bette 请问HAVE SB DONE 不表示现在完成时 when you grow up,为什么不是when you have grown up Given more attention,the trees could have grown better.为什么句首 Given more attention,the tree could have grown better中为什么用过去 I have never thought about it 为什么要用现在完成时呢 不加have可以吗 They have done all they could "to help" him.为什么是"to help"? __(give)more attention,the trees could have grown better.