请教专家：
Iwas being tested for a driving licence for the third time. I had been asked todrive in heavy traffic and had done so successfully. After having beeninstructed to drive out of town, I began to acquire confidence. Sure that I hadpassed, I was almost beginning to enjoy my test. The examiner must have beenpleased with my performance, for he smiled and said. 'Just one more thing,Mr.Eames. Let us suppose that a child suddenly crosses the road in front ofyou. As soon as I tap on the window, you must sTOP within five feet.' Icontinued driving and after some time, the examiner tapped loudly, Though thesound could be heard clearly, it took me a long time to react. I suddenlypressed the brake pedal and we were both thrown forward. The examiner looked atme sadly. 'Mr.Eames,' he said, in a mournful voice, 'you have just killed thatchild!'
1)I had been asked to drive in heavy traffic and had done so successfully. 这里一上来就用过去完成时，是由于参照后面一句的过去时间 I beganto...对吗？
2)The examiner must have been pleased with my performance - 这里既能理解成作者在当时（在过去）对更早的过去的推断，也能理解成作者在写这篇文章的时候，对过去（当时）的推断。对吗？
3)Though the sound could be heard clearly，既然当时能了解听见，为何不是was ableto 呢？
1 过去完成时的用法是依据第一句的过去进行时。第一句交代故事的背景，即作者当时正在驾驶证考试的路考过程中。第二句的过去完成时表示故事发生的时候在市区人多的地方的路考与结束了。
2 must have been pleased 是作者目前的推断，be pleased with为系表结构表示状况。目前对过去状况的推断must后后接不定式完成体。若是作者当时推断当时的状况，情态动词后的不定式应该用一般体而不是完成体。另外，站在过去立场进行推断，情态动词应该用过去形式，而must没过去形式。所以一般要理解这是站在目前的立场进行推断。
3 could在此表示考官敲车窗的声音足够了解，能让他听到。并非表示能力。could用完全正确，为何必须要用was able to do呢？was able to do 表示一个人得以做成某事、设法做成了某事，一般这种事情都涉及主语的能力，需要克服肯定的困难和障碍。所以英文解释为managed to do something, succeeded in doing something. 哪种手到擒来、易如反掌就能做的事是不会用was able to这把牛刀去杀鸡的，打蚊子不需要高射炮的。所以要正确理解could表示可能性的使用方法，不要滥用was able to do。
