【问】 The cave might never have been discovered had not the entrance been spotted by the distinguished French potholer，Berger. (New Concept English，Book3，L. 42)

我不理解had not the entrance been spotted的结构。

【答】 had not the entrance been spotted是个无连词if的条件从句，它等于if the entrance hadnot been spotted...(如果不是法国著名洞穴探险家波格发现了这个入口)。这个例句表明，无连词条件从句可以放在主句之前，也可以放在主句之后(参见Had he been，should，were)。请做下面的英语试题：

1. The millions of calculations involved，had they been done by hand，____all practicalvalue by the time they were finished.

A. could lose B. would have lost

C. might lose D. ought to have lose(攻读硕士学位研究生入学考试英语试题，1994)

2. They are the ones who assert that a better bridge could have been built have we hadtheir assistance. (TOEFL，72，10)

3.____，John would not have failed.

A. If he has listened to me B. Had he listened to me

C. If he listened to me D. As soon as he listened to me(TOEFL，79.5—8)

(参见 conditional clause without a conjunction)