交流电的大小是随着时间按不规则曲线而变化的。
参考答案：错
把一个高为30厘米的圆锥形容器盛满水，倒入和它等底的圆柱形容器里，水面的高度是（ ）厘米．
A．10
B．30
C．60
D．90
—Poppy, with Eddie and Hobo, _____ a movie after dinner every evening.
—How interested they are in it! [ ]
A. watches
B. watch
C. are watching
D. is watching
