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问题 选择题
已知a，b均为正数，
1
a
+
4
b
=2，则a+b的取值范围是（　　）
A．[
9
2
，+∞)		B．[1，+∞）C．[9，+∞）D．[8，+∞）
答案

∵a，b均为正数，

1
a
+
4
b
=2，

∴a+b=

1
2
(a+b)(
1
a
+
4
b
)  =
1
2
+
b
2a
+
2a
b
+2

≥

5
2
+2
b
2a
?
2a
b
 
=
9
2
．

则a+b的取值范围是[

9
2
，+∞)

故选A．

选择题

When Helen saw his tutor nod _____ to her, she felt greatly ______ and was convinced that she would be __________ she had been dreaming of .

A．encouragingly; encouraging; as a successful person as

B．astonishingly; encouraged; as successful a person as

C．encouragingly; encouraged; as successful a person as

D．astonishingly; encouraging; as a successful person as
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单项选择题

英文缩写CAI的中文意思是( )。

A．计算机辅助教学

B．计算机辅助制造

C．计算机辅助设计

D．计算机辅助管理
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