10÷（1-25-25），
=10÷15，
=10×5，
=50（千克）；
答：这袋大米重50千克．
(2013·成都七中考前模拟)We were stuck on the way to the scenic spot, otherwise we ________ lots of fun there.
A．had had
B．have had
C．could have had
D．could have
交一交变频器（电压型）和交一直一交变频器各有特点，下列哪项符合交一交变频器的特点？（）
A.换能环节少
B.换流方式为电源电压换流
C.元件数量少
D.电源功率因数高
