简述中央银行业务活动的原则有哪些？

要想使反射光线跟入射光线成直角，入射角应当是______，若使入射光线逐渐靠拢法线，则反射光线将______法线（填“远离”或“靠拢”）．

Buses were not able to go normally on the roads because of the heavy snow and more than

one student  _____ late for school that morning.  [ ]

A. have been

B. has been

C. were

D. was

战略管理的基本特征有哪些？

销售前，对集团客户的了解，主要是从企业内部外部通信需求、企业组织结构、（）、（）方面考虑。

风电机组的启动和停机有手动和（）两种方式