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问题 单项选择题

猪带绦虫的中间宿主是

A．猪和野猪

B．人

C．A牛B

D．牛、羊、猪

E．猪和野生动物

答案

参考答案：C

解析：猪带绦虫的中间宿主是猪，人误食虫卵后亦可为中间宿主。

解答题
画出不等式组
-x+y-2≤0
x+y-4≤0
x-3y+3≤0
表示的平面区域，并求出当x，y分别取何值时z=x2+y2有最大、最小值，并求出最大、最小值．
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选择题

The hostess told us it was _____ that caused her to serve dinner an hour later than usual.    [ ]

A. for our being late      

B. our being late         

C. we were too late  

D. because we were late
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