答案如下
86.What can be done, and now we can do nothing, can only wait.
87.The more scientists understand the human brain, the more they can not answer the question.
88.I tried to give up the business and I found it impossible.
89.In terms of technical and financial resources, his advice sounds feasible.
90.The river was clean, but it had been polluted since the construction of the chemical industry.
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