人是环境的产物，（）是人生存与发展的客观物质条件和思想意识的来源。
A.环境
B.社会
C.学校
D.家庭
参考答案：A
Two fifths of the highway________so far.[ ]
A. has been completed
B. was completed
C. have been completed
D. has completed
用数据传输速率的单位是
A．位/秒
B．字长/秒
C．帧/秒
D．米/秒
