“龙生龙，凤生凤；一母生九子，连母十个样”这两句谚语分别体现生物的什么现象（    ）

和平是美好的，战争是残酷的，一战中伤亡人数最多的战役是（ ）

用括号内所给动词的适当形式填空。
1.We ____(watch) the boys____ (play) basketball on the playground when something strange happened.
2.I don't know what ____(happen)to him just now.
3.Computers are useful to us. But some students only use them____ (play) games.
4.–--Would you mind____(take) photos with me?

5.--- Of course not. When I miss you, I can have a look.

6.You may go to play football as soon as your homework ____ (finish).
7.Middle school students____(tell) not to smoke.   

我国幅员辽阔，各地方言不一致，汉文字却是统一的。这是因为（　　）

下列观点符合我国可持续发展的是（     ）