任务型阅读

    When you are in Hong Kong，you must be very careful in the streets because the traffic drives on the left．It is different from that in other areas of China．If you are the first time to come to Hong Kong，you must look to the right side and then the left before you cross the street．If the traffic lights are red，the traffic must stop．Then people on foot can cross the road carefully．But if the traffic lights are green，the traffic can go，people on foot mustn’t cross．

    When people go to or come from work in the morning and evening，the streets are very busy．

    Traffic is the most dangerous then，especially (尤其)for the children．

    When you go by bus in Hong Kong．you have to be careful，too．You must always remember the traffic moves on the left．So you must be careful．Have a look first，or you will go the wrong way．

    In Hong Kong，there are many big buses with two floors，you can sit on the second floor．From there you can see the view of the whole city well．It’s very interesting．

根据短文内容，回答下列问题。

我国古代哲学认为物质是“阴阳”组成的对立统一体，阴阳之间既相互对立，又相互统一，既相互依存，又相互制约。下列的化学知识点最能体现“阴阳”对立统一体的是（）

一个三棱柱的侧棱垂直于底面，且所有棱长都为a，则此三棱柱的外接球的表面积为（ ）