1. He told Tom that he had passed the driving-test.
句子中的第二个he究竟是指主语还是指Tom，模棱两可。我们可以理解为He had passed the driving-test and he told Tom. 也可理解为He told Tom that Tom had passed the driving-test.
2. I went to see a film last night because she is a star I like.
因为句子中没有涉及第三者，所以很难断定she指代何人。可改为I went to see a film last night because the actress is a star I like.
3. Li Ming was knocked down by a motorbike, but it was not badly hurt.
It指代前面出现过的名词, 这是it的基本用法之一。此句中唯一的名词是motorbike在此是泛指，故不能用it. 若改为Li Ming was knocked down by a motorbike, but was not badly hurt.句子的意思就明了多了。