____ (happiness) can make us become ill, so we should try our best to be happy.
2(x2y+xy)﹣3(x2y﹣xy)﹣4x2y,其中x=1,y=﹣1.
①千里冰封,万里雪飘。
②欲与天公试比高。
③大河上下,顿失滔滔。
④山舞银蛇,原驰蜡象。