_________ he followed my advice, he would have succeeded.
A. When B. If C. Had D. Has
答案应选C，但容易误选B。不能选B，主要是因为时态前后有矛盾。由于主句谓语是would have succeeded，这表明是对过去事实作出的假设，所以从句谓语应该是 had followed，所以，如果选B，句子应该是 if he had followed my advice。但按英语语法，在此类表示虚拟条件的从句中，若有 had, should, were 等词，便可省略 if，而将 had, should, were 提前置于句首。又如：
If he were my friend, I would ask him to lend me some money.= Were he my friend, I would ask him to lend me some money. 假若他是我的朋友，我就会向他借些钱。
If it should rain tomorrow, I should stay indoors.= Should it rain tomorrow, I should stay indoors. 如果明天下雨，我就呆在室内。
If he had asked me, I would have told him. = Had he asked me, I would have told him. 要是他问过我，我就会告诉他了。