put 语法填空during his useful life he often felt he was useless."Alfred Nobel ,"he once wrote to himself,"ought to (put)to death by a kind doctor as soon as ,with a cry ,he entered life."为什么不能用be put 涉及到什么知识?

Question

put 语法填空
during his useful life he often felt he was useless."Alfred Nobel ,"he once wrote to himself,"ought to (put)
to death by a kind doctor as soon as ,with a cry ,he entered life."
为什么不能用be put 涉及到什么知识?

Answer 1

ought to＋have＋过去分词”既可表示本该做而事实上没有做的事,也可以表示惊讶、赞叹等情绪.
其实“情态动词＋have＋过去分词”是很重要的一种句型,除should外,may,might,must,couldn’t,needn’t,ought to等都可以用于这一句型.