把x=2y=-1代入方程2x-3y=a,得
4+3=a,
解得a=7.
Little Tom has got a lot of birthday presents, but he isn’t able to take all of them ___.
A.on time
B.at a time
C.at same time
D.from time to time
中国近代进行教育变革的最根本的原因是[ ]
A.西方先进科技文化大量涌入
B.传统教育与科学制度存在着危害
C.顺应世界的潮流
D.统治阶级想收买人心