I'm sorry I can't answer the question.

很抱歉我无法回答这个问题。

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1. It's difficult to say.很难说。

2. Do you think so? 你这样认为吗？

3. I'd rather not say anything about that.对于这一点我还是不说什么的好？

4. I'm afraid you'd have to ask Dr.Brown about that.这件事恐怕你还得问布朗医生。