A: Excuse me. Is there a ____ near here?

B: Yes, there is.

A: Where is it?

B: It's ____the science museum.

A: Is it____

B: No, it isn't. Go straight to the first crossing and then turn ____

A: OK. I'll ____there. Thanks.

阅读古诗回答问题。
中秋月 苏轼
暮云收尽溢清寒，银汉无声转玉盘。
此生此夜不长好，明月明年何处看

$\sqrt{a^2}$等于（   ）