Tom and Mike are good friends. They are kind to children. They want to find summer jobs. One day Tom tells Mike that Beidaihe Kids Summer Camp needs help with sports, music and computers. They are both very glad to hear(说) this. Tom can play basketball and volleyball, and he can swim, too. Mike can play the violin, the trumpet, the drums and the guitar. Tom and Mike like computers very much. Can they join the Summer Camp?

1979年某地一位农民做裤子卖，一天挣的钱比在地里刨一年还多。远近农民纷纷仿效，这引起了轩然大波。民兵围追堵截，工商税务补税罚款，然而，撵了集中的却撵不了分散的，裤子交易仍在进行。到1984年，该地裤子市场终于名正言顺。结合所学知识，对此认识中不正确的是（   ）

解方程组$\left\{\begin{array}{c}3x+5y=12\\ 3x-15y=-6\end{array}\right.$比较简便的方法为（　　）