1.to play 要改为 playing
What abou doing sth 做某事怎么样?
2.many 要改为 much
water 是不可数名词,不能跟how many 连用.
3.parent 要改为 parents
父母双方用 parents ,parent 指父亲或者母亲
他父母都是工人.
4.violin 前 加 the
西洋乐器前必须加定冠词the
play the violin 拉小提琴
5.them 要改为 theirs
用名词性物主代词.
theirs =their box
你的箱子比他们的（箱子）重.