.--Your parents were anxious about you. You home without saying a word. It’s my fault.

问题补充：

.--Your parents were anxious about you. You home without saying a word.

-- It’s my fault.

A. mustn’t be

B. shouldn’t have left

C. needn’t have left

D. couldn’t have left

答案：

A. mustn’t be

(答案→)B. shouldn’t have left

C. needn’t have left

D. couldn’t have left

解析：考查虚拟语气.句意,你的父母很担心你.你不应该没说一句话就离家了.——那是我的失误。可知问句中表示的是对过去的推测。故选B最符合语境。