来自同一总体的两样本，下列哪个指标小的样本均数估计总体均数时更可靠？（）
A．S[*]
B．CV
C．S
D．t0.05,v·S
E．
参考答案：A
We have been in China _____ three years. We like it very much. [ ]
A. in
B. since
C. for
当辐射投射到固液表面是表面辐射，投射到气体表面是（）
