表语从句连接词：that / whether /as if /as though连接代词：who / whom / whose / which / what 连接副词：when / where / why / how / because 1) that 在从句中仅起连接作用，无实际意义，在句中不做任何成分，不能省略。2) whether在表语从句中表 是否 但不充当句子的成分。if 不能 引导表语从句.如:1. What the doctor really doubts is whether my mother will recover from the serious disease soon.2. The question is whether it is worth doing. 3) What在表语从句中充当主语宾语表语，表示什么，什么样子，的人或事.1. The question is what caused the accident. 2. That mountain is no l
