题干
四、it类
. Everyone knows that _______ is dangerous to play with fire, but _______ is difficult is to prevent children from playing with fire.
A：it, it
B：what, what
C：it, what
D：what, it
答案(点此获取答案解析）
D
2AB3(g)反应来说，下列所表示的化学反应速率中最大的是
，那么
的值是（ ）
