蝶窦炎引起的眶尖综合征的临床表现可有（）
A.上睑下垂
B.眶周皮肤感觉障碍
C.复视
D.眼球充血
E.眶内蜂窝织炎
参考答案：A, B, C, D
Which of the following most accurately describes the competitive structure that is characterized by a firm that operates with the lowest average total cost and has the capacity to produce all of an industry's output（）
A. Oligopoly.
B. Competitive monopoly.
C. Natural monopoly.
家蝇的成蝇足有（）对。
