(2)whether/if:表示是否,在宾语从句中不做成分。
I don't know if /whether he still lives here after so many years. 我不知道这么多年后,他是否还住在这里。
(3)连接代词:what, which, who, whom, whose(在宾语从句中做主、宾、表和定语)
连接副词:where, when, how, why(在宾语从句中做状语)
The small children don't know what is in their stockings.(what 在宾语从句中做主语)
Could you tell me why you were late for the meeting this morning?(why 在宾语从句中做原因状语)