c.fast.牢牢地。make sure the door is _ shut before you leave.本句意思是出门时一定要保证牢牢锁上门。本句的考试点在fast和fastly. 英语没有 fastly 这个单词.所以答案只能是fast. fast 本身即是 形容词,也是 副词. fast 是一个所谓 “非常规” 副词, 其他这种形容词变非常规副词的单词有 hard bad 比如 he is a fast runner (形容词) / he runs fast (副词) she is a hard worker (形容词) / she works hard (副词) it has a bad smell (形容词) / it smells bad (副词)