当目标成分为次级代谢产物时，应选择哪个阶段的微生物菌体作为原料（）。
A.指数生长期
B.减速期前期
C.减速期后期
D.静止期前期
参考答案：C
一个容量为n的样本，分成若干组，已知某组频数和频率分别为36和0.25，则n=______．
Tomorrow is Tom's birthday. Have you got any idea________ the party is to be held? [ ]
A. what
B. which
C. that
D. where
