题干
—Why are you looking for Mary in a hurry, John?
—The boss is wondering where she _____ and how long she ______ there.
A：has been； has been
B：has gone； has gone
C：has been； has gone
D：has gone； has been
答案(点此获取答案解析）
D
”和“ 
”分别代表两种不同的单质分子A2和B2，它们在一定条件下能发生化学反应，其反应的微观示意图如图． 
