笔袋13元一个，妈妈为我和2个表妹各买了一个，共用多少元？
13×（1+2）=39（元）
Waste paper _______ everywhere. It's our duty to keep the school clean. [ ]
A. throws
B. are thrown
C. shouldn't be thrown
D. should be thrown
下面哪几种是jquery中表单的对象属性（）
A、：checked
B、：enabled
C、：disabled
D、：selected
