脑脊液来自鼻顶者，瘘孔在（）
A.筛骨筛板
B.额窦
C.蝶窦
D.鼓室或乳突
E.颅中窝
参考答案：A
在市场经济活动中，为了获取利益，可以采取各种手段，与同行竞争。
It （） around six o'clock when I drove back yesterday because it was already dark.
A. must have been
B. must be
C. was to be
D. had to be
