______, there was no hope of her being able to sleep.
    A．As she was exhausted                  B．Exhausted as she was
    C．Exhausted as was she                   D．As was exhausted she

设f(x)在(a，b)内有连续的二阶导数，x0∈(a，b)，若f(x)满足( )，则f(x)在x0取到极小值。 A．f(x0)＞0，f(x0)=0 B．f(x0)＜0，f(x0)=0 C．F(x0)=0，f(x0)＞0 D．f(x0)=0，f(x0)＜0

A.f'(x₀)＞0，f''(x₀)=0
B.f'(x₀)＜0，f''(x₀)=0

C.F'(x₀)=0，f''(x₀)＞0
D.f'(x₀)=0，f''(x₀

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心理物理学中建立等级量表的主要方法有（）。

A.等级排列法
B.数量估计法
C.差别阈限法
D.对偶比较法

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