下列结构中不存在染色体的是（　  ）

梭伦在当选执政官前，曾经赋诗说：“我注目凝视，悲哀充溢着我的心，这是爱奥尼亚（雅典）最古老的地方，竟至陷入绝境。”梭伦所说的雅典“陷入绝境”主要因为（    ）

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.