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?

《环境空气质量标准》新增PM2.5指标，PM2.5是指直径小于或等于2.5ｕｍ的颗粒物。为实现空气质量达标，合理的做法是（____）

A.煤炭直接燃烧                 B.秸秆焚烧还田

C.开发清洁能源                 D.____；

我们终身学习的重要基础是哪个阶段的学习，它将使我们终身受益（      ）

如果${\log }_3^m+{\log }_3^n=4$，那么$m+n$的最小值是（   ）

下列有关基因重组的叙述，正确的是（    ）