对于均质流体来说，单位体积内所含有的质量叫做（）。
A.粘度
B.密度
C.比重
D.重度
参考答案：B
He was so pleased with all _____ we had done for him _____ he wrote us a letter to praise us for it.
A．that; that
B．what; that
C．that; what
D．what; what
耐青霉素金葡萄感染治疗宜选（）
A.青霉素V
B.苯唑西林
C.氨苄西林
D.羧苄西林
E.磺苄西林
