All his attention________on the computer game he was playing,so he even didn't notice his mother

enter the room. [ ]

A. has been fixed

B. was fixing

C. was fixed  

D. fixed

时间序列中对应于具体时问的指标数值是（）。

A.发展速度

B.平均发展水平

C.发展水平

D.动态平均数