间体在G+和G-细菌中间同样发达。
参考答案：错
It was _____ back home after he finished the report.[ ]
A. not until midnight did he go
B. until midnight that he didn't go
C. not until midnight that he went
D. until midnight when he didn't went
点M在曲线AOB上运动。曲线由AO、OB两段圆弧组成。AO段曲率半径R1=18m，OB段曲率半径R2=24m，取两圆弧交接点O为原点，并规定正负方向如图所示。已知点M的运动方程为s=3+4t-t2（t以秒计，s以米计）。则t=5秒时点M的加速度大小为（）。
A.1.5m/s2
B.2m/s2
C.2√2m/s2
D.4m/s2
