题目

不同生物含有的核酸种类不同。真核生物同时含有DNA和RNA，病毒体内含有DNA或RNA，下列各种生物中关于碱基、核苷酸种类的描述正确的是( )  ABCD 口腔上皮细胞洋葱叶肉细胞脊髓灰质炎病毒豌豆根毛细胞 碱基5种5种4种8种 核苷酸5种8种8种8种   答案：B 阅读短文，然后根据内容回答所提问题。 　　Welcome to the Eiffel Tower! It was built by Gustave Eiffel, a famous French engineer．The Tower was finished in 1889．It is made of iron．There are about 18, 000 different parts altogether．The height of the Tower is 320 metres．It is still the highest building in Paris． 　　At first, some people did not like the Tower．They said that it was very ugly．But after a few years, it became very popular．The Tower has lifts which go up to the top．There is a very good view of Paris from there．On a clear day, you can see for more than 30 miles．If you don't want to go by lift, you can walk up the steps, but remember that there are 1, 792 steps up to the top． 　　The Tower is repainted every seven years．It is brown in colour．About 45 tonnes of paint are needed to repaint it．Some amazing things have happened to the Eiffel Tower over the years．Once, an elephant walked up to the first level．A man has cycled down all the steps．And in 1984, tow people jumped off the top, and used parachutes to get down safely．