如何分析这个疑问句

有这样一道题：

What do you imagine _________ him from going?

A. to prevent B. preventing C. to have prevented D. prevented

此题答案选D，其中的 do you imagine 为插入成分，如果去掉的话，显然prevented为句子的谓语。以下各例中的 do you think (suppose, imagine, guess, etc) 也是插入成分，其后接的句子应用陈述句词序：

Who do you think he will marry? 你认为他会同谁结婚？

What do you think we should give her? 你认为我们该给她点什么呢？

When do you believe he will come? 你认为他会什么时候来？

What do you guess he wants to buy? 你猜他想买什么呢？