447.Mr.Green once _______ English at Cambridge University for 5 years and now is a speaker.
No wonder he ______ perfect English.
A.had taught；spoke
B.taught；speaks
C.is teaching；has spoken
D.has been teaching；will speak
448.Why did you leave the water running in the sink?
Heavens!I guess I _____ to turn it off.
A.forgot
B.have forgotten
C.will forget
D.had forgotten
447.答案是B；根据once暗示，第1空用过去时;第2空说明现状。
448.答案是A;根据语境，应该为刚才忘记关水龙头了。
