问题
选择题
---Lucy is a _______girl.
---Yes, she always studies hard at night.
A．hard-work
B．hard-working
C．hard-worked
D．hard-works
答案
答案：B
题目分析：句意：露西是个勤奋的女孩。勤奋的，努力的hard-working，故选B。
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---Lucy is a _______girl.
---Yes, she always studies hard at night.
A．hard-work
B．hard-working
C．hard-worked
D．hard-works
答案：B
题目分析：句意：露西是个勤奋的女孩。勤奋的，努力的hard-working，故选B。
，则下列条件中能保证f(x1，y1)＜f(x2，y2)的是