（）是精矿中金属的重量与原矿中该金属的重量之比的百分数。
参考答案：回收率
Joe, my close friend, moved to Beijing 10 years ago, and I ________ him since then. [ ]
A. don't see
B. didn't see
C. haven't seen
D. won't see
满族在隋唐时期称为（）。
A.女真
B.靺鞨
C.满洲
D.女真
