It was spring _____ my mother bought me a mountain bike and I started learning cycling. [ ]

A. that

B. when

C. in which

D. where

在一定抽样精度的要求下，（）

A.总体越大，样本也越大

B.样本不按比例地随总体增大而增大

C.总体地异质性程度越小，样本的规模越大

D.总体的同质性程度越大，样本的规模越大