the boy couldn’t enter his house. A. Since the key has lost B. The key been lost C. Lost

问题补充：

, the boy couldn’t enter his house.

A. Since the key has lost

B. The key been lost

C. Lost the key

D. Having lost the key

答案：

A. Since the key has lost

B. The key been lost

C. Lost the key

(答案→)D. Having lost the key

解析：考查非谓语动词。主语the boy与lose之间是主谓关系，所以用现在分词，且分词的动作发生在谓语动词之前，所以用现在分词的完成式。句意：丢了钥匙之后这个小男孩不能进入他的房子。所以选D。