A:Because he was too busy to go to the bookstore.
B:Because the bookstore closed before he arrived.
C:Because the books were sold out before he arrived.
我们在教室的各个方向都能看到黑板上的字,这是光照到字表面发生了____现象;而学习或工作用的台灯上有一个灯罩(如图所示),其中作用是利用光的____定律将光线尽量集中到需要照射的地方,因此灯罩内表面应尽量____(填“光滑”或“粗糙”).
连词成句you, do ,what, do, weekend, the, at, Sam? ____
—Chongqing is ____________ than ____________ city in the north of China.
—I think so. It's the hottest city ____________ the southwest of China.