I can't make out who it is.
我弄不明白到底是谁。
----------------------------------------------------------------------
今天的几个句子还是有关表达不确定的：1.I should think I heard his voice. 我想我听见了他的声音。2.It's hard to tell. 很难说。3. I suppose it could be Mary.我想可能是玛丽吧。4. Perhaps the answer is not to do it.也许答案是不去做。