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【简答题】
下列命题中： ①函数 f(x)=x+ 2 x (x∈(0，1)) 的最小值是 2 2 ； ②对于任意实数x，有f（-x）=-f（x），g（-x）=g（x）且x＞0时，f′（x）＞0，g′（x）＞0，则x＜0时，f′（x）＞g′（x）； ③如果y=f（x）是可导函数，则f′（x 0 ）=0是函数y=f（x）在x=x 0 处取到极值的必要不充分条件； ④已知存在实数x使得不等式|x+1|-|x-1|≤a成立，则实数a的取值范围是a≥2． 其中正确的命题是______．
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举一反三
【简答题】central fovea
【单选题】Could you please tell me _____? [ ]
A.
where the Grand Central Station is
B.
how far the Grand Central Station was
C.
how can we get to the Grand Central Station
D.
when was the Grand Central Station built
【单选题】Which is NOT true about the central area?A．It was often hot and rainy in central areas.###
A.
Which is NOT true about the central area? A．It was often hot and rainy in central areas.
B.
Most of the Mayan population lived in this area.
C.
There were few plants or trees in this area.
D.
Most of the cultural accomplishments came from this area.
【单选题】Which of the following tips for central idea is false?
A.
Make sure the central idea is not too specific.
B.
Express the central idea as a full sentence.
C.
State the central idea as a declarative sentence, not as a question.
D.
Avoid figurative language in the central idea.
【单选题】Which of the following tips for central idea is false?
A.
make sure the central idea is not too specific
B.
Express the central idea as a full sentence.
C.
State the central idea as a declarative sentence, not as a question.
D.
Avoid figurative language in the central idea.
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