题目

下面利用凸透镜原理制成的是（     ）。 A . 放大镜 B . 太阳灶 C . 哈哈镜 答案：AThe USA _________ on several countries in the past years, which reminds us that a nation must be strong if it _________．A.has started war, is to surviveB.started war, is going to surviveC.had started war, will surviveD.has started war, is about to survive