____ their service, the workers of the hotel are active in learning English. [ ]

A. Improving

B. To improve

C. Improve

D. Having improved

两样本均数比较的t检验，t＜t_0.05/2，v，则正确结论是（）。

A．两样本均数不相等

B．两总体均数不相等

C．两样本均数相等

D．两总体均数相等

E．两总体均数差别很小