阅读下列短文，从每题所给的几个选项中，选出最佳选项。

Do you know something about the holiday camps in Hong Kong? The students in Hong Kong used to take part in an English holiday camp in their holidays. And their parents weren’t with them, though they were very young.Now they still enjoy taking part in many kinds of holiday camps without their parents. Many parents let their children take part in some kinds of holiday camps in order to learn some practical knowledge in their life and also learn some knowledge about living skills, science, reading and writing ... The most important for the children is to learn to look after themselves. Holiday camps in Hong Kong are not so expensive. Most families can afford to send their children there for further study or for making their bodies strong.

It is said that students in Hong Kong have much knowledge about many things. Perhaps it has something to do with all kinds of holiday camps.

在20世纪90年代，陕西章台出土了一些秦代封泥（密封信件文书时加盖了印章的泥块），上面有上郡．代郡．邯郸等郡名和蓝田等县名。这一发现可以印证秦朝（   ）

使用显微镜时，“观察”操作步骤正确的是（　　）

①转动粗准焦螺旋，使镜筒缓缓下降，直到物镜接近玻片标本为止；

②左眼向目镜内看，右眼睁开；

③把要观察的玻片标本放在载物台上，用压片夹夹往；

④反方向转动粗准焦螺旋，使镜筒缓缓上升；

⑤略微转动细准焦螺旋．