阅读理解

    I'm Li Ming．The holidays always make me happy．Last summer holiday,I went to Paris with my mother by plane．We went there to visit my uncle．He met us at the airport．

    My uncle took us to visit the Louvre Museum by underground．I saw a lot of famous things．I enjoyed many old pictures in it．The pictures were very creative(有创意的)．We also visited the Eiffel Tower．It is the famous symbol(标志)of Paris．One evening，my uncle took us to eat good food and go shopping．My mother bought many clothes-some for her,and some for my sister．

We stayed in Paris for about half a month.The trip gave me lots of fun.I will remember it.

根据材料内容选择最佳答案。

在调查某小麦种群时发现T（抗锈病）对t（易感染）为显性，在自然情况下该小麦种群可以自由传粉，据统计TT为20%，Tt为60%，tt为20%，该小麦种群突然大面积感染锈病，致使全部的易感染小麦在开花之前全部死亡．计算该小麦在感染锈病之前与感染锈病之后基因T的频率分别是多少？（　　）

—Tom_____.