To everyone's surprise, Alex play chess very well when he was only four.
A:might
B:should
C:would
D:could
80-60=( )
如图所示,轻弹簧下悬挂一个条形磁铁,磁铁下方有一通电螺线管,如图所示,为使悬挂磁铁的轻弹簧伸得最长,下列措施正确的是