问题补充:
He must have gone out. I heard the noise of the door when I was still in bed.
A. being locked
B. to lock
C. locking
D. having locked
答案:
(答案→)A. being locked
B. to lock
C. locking
D. having locked
解析:考查非谓语动词和固定用法。句意“他一定是出去了。当我没起床时,我就听见了锁门声。”door和lock之间是被动关系,应该用被动语态。hear sb./sth. doing sth.“听到正在做某事”。故选A。