视网膜神经节细胞的同心圆式感受野形成的生理学机制是（）.
A.侧抑制
B.前抑制
C.正反馈
D.负反馈
参考答案：A
–You’re coughing badly, Martin. Why not give up smoking?
--Give up smoking? Easier said than done, Amy. Once you _________ the habit of smoking, it is very had for you to _________.
A．keep up; break it away
B．take up; drop it out
C．pick up; get rid of it
D．build up; do away with it
下列措施哪一项不能增加金属和瓷的结合力
A．金属表面的清洁B．金属表面凹凸不平C．底瓷熔融的流动性好D．获得良好的润湿界面E．加入微量非贵金属元素
