题目

I think ___ good knowledge of English is ___ great help when you are traveling around the world. A. X，a     B. a，a     C. a，the     D. a，x 答案：A 解析: a knowledge of 指哪一门学科知识，这个时候可数；动词用做名词，前面经常使用冠词a .下列物质可用作复合肥料的是A.NH4HCO3B.KNO3C.Ca3(PO4)2D.K2SO4