大禹治水曾三过家门而不入，他所治的“水”是指（　　）

____

阅读短文，判断正确还是错误。

A letter

Here is a letter from Jim to his friend in the USA

Dear Lily:

    I am in China now. I go to school five days a week. The school and the food are good here. I have some Chinese friends. They are all very friendly to me. On Saturdays and Sundays we stay at home. In the afternoon we play games. My Chinese friends like English very much. They ask me to teach them English and they teach me Chinese. I like staying here.

    Please write soon!

在﹣ $\sqrt{2}$ ，0. $\stackrel{\cdot }{3}\stackrel{\cdot }{1}$ ， $\frac{\pi }{3}$ ， $\frac{1}{7}$ ，0.80108中，无理数的个数为（   ）