杜仲、知母炮制的适宜方法是（） A．酒炙 B．盐炙 C．蒸法 D．煮法 E．醋炙

要介绍碳酸盐岩油气层酸化时，盐酸与碳酸盐岩的反应步骤。

He expressed his gratitude to his headteacher, without _____ help he wouldn't have made such great progress

in his studies. [ ]

A. whose

B. his

C. whom

D. which

我国的经济与社会发展规划具有指导性、宏观性、战略性和( )的特点。

A．政策性

B．纲领性

C．统筹性

D．统一性

              is her hair? It is black .[ ]

A. what  color

B. What class  

C. What grade

纳税人已开具的发票存根联和发票登记簿的保存期限是（）年。

A.3

B.5

C.15

D.25