混凝土泵车作业中需要移动车身时,应将上段布料杆折叠固定,移动速度不得超过()km/h。
A.20
B.15
C.10
D.5
参考答案:C
分子式为C8H10的烃的所有同分异构体中,属于苯的同系物的有几种( )
A.2种
B.3种
C.4种
D.5种
Why don’t you put the meat in the fridge?It will________fresh for several days.[ ]
A.be stayed
B.stay
C.be staying
D.have stayed