---What did you say to Julia? I saw her crying in the dormitory aloneIt my fault. W

问题补充：

---What did you say to Julia? I saw her crying in the dormitory alone.

--- It my fault. We talked happily when I was with her in the classroom.

A. mustn’t have been

B. should have been

C. shouldn’t have been

D. couldn’t have been

答案：

A. mustn’t have been

B. should have been

C. shouldn’t have been

(答案→)D. couldn’t have been

解析：考查情态动词。句意为：上句是你对Julia说什么了？ 我看见她一个人在宿舍哭呢； 下句是不可能是我的错，当我和她在教室的时候我们谈的很高兴。couldn’t have done表示不可能，所以选D 。