楼梯的建筑构造要求中，疏散用楼梯和疏散通道上的阶梯不宜采用( )和扇形踏步。
A．一般楼梯B．螺旋楼梯C．电梯D．梯形楼梯
参考答案：B
将一正电荷从电场中的A点移到B点，电场力做了2.4×10-6J的功，已知AB两点的电势差为240V，那么该正电荷的电量为______C，电荷的电势能______（填“增加”或“减少”）了______J．
We thought of selling this old furniture, but we've decided to ____ it. It might be valuable.
A. hold on to
B. keep up with
C. turn to
D. look after
