The growing speed of a plant is influenced by a number of factors, _______ are beyond our control.

A．most of them

B．most of which

C．most of what

D．most of that

（1）求回路的最大电流．

（2）当滑行过程中电阻上产生的热量为Q时，杆ab的加速度多大？

（3）杆ab从开始运动到停下共滑行了多少距离？