阅读理解:阅读下列短文，然后从每题所给的四个选项(A、B、 C、和D)中，选出最佳选项。

    Mr. and Mrs. Green were going on their vacation with their children, and they had to arrive at the airport before 11:40 the next morning. “It takes us thirty minutes to get there in a car,”Mr. Green said, “so we must get ready before eleven o'clock. Don't be late.”

At ten fifty, all of them were busy doing something, but Mrs. Green wasn't. She sat quietly in a chair in the garden and enjoyed the good weather.

Mr. Green and the children were surprised, but Mrs. Green said, “Don't worry! Before I went to bed last night. I made all our clocks and watches twenty minutes ahead(提前). Now we can get to the airport early.”

在实数范围内,下列各式一定不成立的有(    )
(1)$\sqrt{a^2+1}$=0; (2)$\sqrt{a-1}$+a=0; (3)$\sqrt{2a-3}$+$\sqrt{3-2a}$=0;(4)$\frac{1}{a-2}$=0.