图中表示静止在斜面上的物体所受的重力是（  ）

如下表示人体内气体交换的过程，其中能发生气体交换的是（　　） 空气 呼吸道 肺泡 血液 组织细胞．

阅读理解

    Being outgoing is good for your life. Those who are more outgoing may have more fun in life. In fact, being outgoing is not so hard as you think. Even shy people can be outgoing.

    You can start becoming outgoing with your best friends or a group of friends. But the real challenge（挑战）comes when you meet strange people. Smile more, and usually they will return your smile. In this way, you may have some more talks.

    Start a talk. Just a simple "Hello" or "How is it going” is a good start. If you want to make interesting talks, you should read news in the newspapers and prepare（准备）your views, or surf the Internet for new information and then keep that in mind.

    The easier way to become more outgoing is to go out. This is also the most important step. Go to a park, the beach, a club, a party or any other places that you think can be fun, and you may make new friends there.

要使视野中单个细胞最大，你认为应选用的显微镜镜头组合是（　　）

下列属于光的直线传播形所成的现象是（）