把圆柱的底面平均分成许多相等的扇形,然后把圆柱切开,可以拼成一个近似的( )。它的底面积等于圆柱的( ),它的高就是圆柱的( )。
长方体;底面积;高
若z=1+2i,则=()。
A.1
B.-1
C.i
D.-i
The government has taken some measures to solve the shortage of electricity, but it may be some time _______ the situation improves.
A.since
B.when
C.unless
D.before