在 $\frac{3}{9}$ ＋ $\frac{6}{11}$ ＋ $\frac{6}{9}$ ＋ $\frac{5}{11}$ 这个算式中，用加法（   ）比较简便。

    John gets up early from Monday to Saturday, because he must go to school before 7:30 on weekdays(工作日) and go to Drawing Club at 8:00 on Saturday mornings. He usually goes to the bookshop on Saturday afternoon, and after dinner he watches TV until(直到) midnight(午夜).

    He doesn't get up early on Sundays. John's parents both work on Sundays. John always watches TV after he gets up. Then he usually goes to KFC to have a hamburger and some juice for lunch. After that, he goes back home and starts to play computer games until his parents come back. He does his homework after dinner. He usually has lots of weekend homework, so he must spend three hours on it. He usually goes to bed at about 11:00 p.m. on Sundays. He often complains(抱怨) he has too much homework to do.

根据短文内容，选择最佳答案。

（2015•大连）如图所示，把装水的大烧杯放在水平升降台上，将一轻质玻璃杯倒扣在水中，玻璃杯内封闭一些气体，玻璃杯底用支架固定，支架在水中部分的体积忽略不计，水面都是静止的．将升降台缓慢升起一定高度（玻璃杯口没有接触大烧杯底部），水面静止后，下列说法正确的是（　　）