月经的第25～28天，称为
A．增生期B．分泌期C．月经前期D．月经期E．初潮
参考答案：C
He has only _______ friends , so he often plays by himself. [ ]
A. a few
B. few
C. a little
D. little
蒸汽溶解携带的硅酸会沉积在（）。
A.过热器管壁上
B.气轮机叶片上
C.过热器和气轮机内
