Expecting to wait for hours,she brought along abook to read.

以上面医生和老师的句子为例，他其实是两个句子：She was expected to be a doctor. She became a teacher instead. 这是两个简单句。如果想要合成一句话，有两个选择1. 用连词 She was expected to be a doctor but she became a teacher instead. 这个句子仍然是简单局。2. 用从句，将分词提前，去掉主语和谓语，变成从句，即， Expected to be a doctor, she became a teacher. 都是同一个意思，但这句话句式比较复杂，比简单句要有水平些。在这种从句中，动名词是表主动， 过去分词表被动，不需要谓语动词。