根据汉语意思完成英语句子。

1. 预订机票时，你必须出示身份证。

    You must show your ___________  when you book an air ticket.

2. 天气预报说本周末天气凉爽，去卧虎山水库钓鱼怎么样?

    The weather report said it would be cool this weekend.___________ going to

     Wohushan Reservoir to fish?

3. 在解放军的帮助下，汶川人民已经克服了很多困难。

    The people in Wenchuan ___________ a lot of difficulties with the help  of the PLA.

4. 在2008年奥运会开幕式上人们将看到一万张世界各地孩子的笑脸，因为我们将孩子的笑容视为

   世界光明未来的象征。

     People will see ten thousand smiling faces from children all over the world at the opening ceremony

     of the 2008 Olympics. Because kids' smile ___________  a symbol of the bright future  of  the world.