我国城市地下水下降的主要原因是().
A.降雨减少
B.城市化过程中不透水地面的增加
C.森林植被被破坏
D.过量的开采地下水
参考答案:D
Ever since he caught the N1H1, Peter _____ so much pain that he is coughing day and night.[ ]
A. suffered from
B. has suffered from
C. suffers from
D. were suffering from
硫酸二甲酯与苯酚制备苯甲醚属于N-烷基化工艺。