洗衣机按洗涤方式不同可分为（）洗衣机、（）洗衣机和（）学洗衣机。
参考答案：波轮式；滚筒式；摆动式
I was so excited last night that it was a long time _____I got to sleep.[ ]
A. that
B. since
C. before
D. when
调度集中的主要优点有哪些？
