线路速度100km/h,采用反向曲线变更线间距可不设缓和曲线的最小圆曲线半径为()。
A、4000m
B、5000m
C、10000m
D、12800m
参考答案:A
— Do you think we should accept that offer?
— Yes, we should, for we ___such bad luck up till now, and time __ out. [ ]
A. have had; is running
B. had; is running
C. have; has been run
D. have had; has been run
核糖体的大小亚基常游离于细胞质中,以各自单体的形式存在。()