各邮政代理保险网点请领空白凭证数量以不超过()的使用量为限。(五级、四级)
A、七天
B、半个月
C、一个月
D、三个月
参考答案:B
You can not imagine the difficulty they had ____ the problem. It isn't ____ easy. [ ]
A. to solve; so
B. solved; so
C. solving; that
D. solved; that
在保持温度不变的条件下,同种材料制成粗细相同的不等长的导线,其电阻与长度成反比。