题干
John's never flown to Canada, _______?
A：is he
B：isn't he
C：has he
D：hasn't he
答案(点此获取答案解析）
C
John's never flown to Canada, _______?
A：is he
B：isn't he
C：has he
D：hasn't he
学方程式如下：SiCl4(g)＋2H2(g)
Si(s)＋4HCl(g)；ΔH＝＋Q kJ·mol－1(Q>0) ，某温度、压强下，将一定量反应物通入密闭容器进行以上反应(此条件下为可逆反应)，下列叙述正确的是( )
