蛔虫在人体的小肠内不会被消化的原因是（　　）

我国是世界文明古国之一，其重要标志是（    ）

①印刷术 ②指南针 ③火药 ④造纸术 ⑤甲骨文的发现

根据短文内容, 选择正确答案。

      Bats are the only “flying animals” in the world. They can't see very well. We often hear “as blind as a bat”. Yet they have no trouble flying on the darkest nights and finding their ways round. How can bats fly and see at night? They fly by radar(雷达).

      The bat's radar system(系统) works the same way as the radar in ships and planes. As a bat flies through the air, it makes a sound. If the sound hits things, it will come back and the bat’s ears will receive the message. In this way the bat is able to know where the things are. Bats go out for food at night. In the daytime they hang in some dark places. Some people think bats are bad animals. In fact they are useful animals.

美国独立战争的转折点是（    ）