题目

More and more US students begin to learn Chinese at school ___________ it is very difficult. A. so                     B. before               C. until                  D. though 答案：D我国设施蔬菜的栽培面积已超过多少（ ）A.15000000hm2B.16000000hm2C.10000000hm2D.12000000hm2