81的平方根是（     ）

关于的不等式ax﹣b＞0的解集是（1，+∞），则关于x的不等式 $\frac{ax+b}{x-2}\le 3a-b$ 的解集用区间表示为____．

The desk that ____ clean so I could do homework was always surrounded with bowls of bad milk, old magazines and so on.

煤、石油、天然气等化石燃料在地球上的蕴藏量是有限的，因此，我们要（1）节约能源；（2）开发新能源；（3）利用电解水的方法生产氢气来补充能源的不足；（4）用酒精作能源．你认为最合理的是（　　）

     Tom and Mike are good friends. They are good with children. They want to find jobs in summer vacation. This Friday Tom tells Mike that Sunson School Trip needs teachers to help with sports, music and computer. Mike is glad to know that.
    Tom can play basketball, volleyball, and he can swim. Mike can play the violin, the trumpet, the drums and the guitar, and he can swim,too. Tom and Mike like computers very much. Can they join Sunson School Trip?