用所给的适当形式填空。 1.At about eight o'clock, the teacher began to _______ (teach) us how to learn English. 2.I _______ (receive) a special gift last night. 3.There must be someting that _______ (happen) yesterday. 4.Why didn't you _______ (invite) Xiao Ming to come here? 5.I _______ (sleep) when the teacher came in.