题干
It's important_______ the piano well.
A：of him to play
B：for him to play
C：of him playing
D：for him playing
答案(点此获取答案解析）
B
It's important_______ the piano well.
A：of him to play
B：for him to play
C：of him playing
D：for him playing
2Z(g)，到达平衡后，Y的体积分数为a%，然后再向容器中通入2 mol Z，保持在恒温恒压下反应，当达到新的平衡时，Y的体积分数为b%。则a与b的关系是