阅读理解
B
    I went to Paris last August．I went there with my friend Jeff．We went by train．We stayed for five days in a small hotel in the center of Paris. The hotel was not expensive .Our room was OK—it was old，but very clean.
    In the mornings we visited all the famous tourist sights(著名的旅游景点)and museums．The Louvre Museum was my favorite ! We usually had some bread for lunch in a park．In the afternoons we walked around Paris．We took a lot of photos! And we had crepes! They were delicious! After a little sleep and a shower, in the evenings．We had dinner in small restaurants and then we went to pubs(酒吧)．We met very interesting people! We also made some good friends．
    We didn't buy any gifts．Everything was very expensive．But we sent(邮寄)very beautiful postcards(明信片)to our friends．We had a lot of fun ! It was an excellent holiday!
根据材料内容选择最佳答案。

家兔之所以能保持前后代染色体数目的恒定，是因为其在生殖过程中要进行 (     )

万卡特拉曼一莱马克里斯南、托马斯一施泰茨和阿达一尤纳斯三位科学家因“对核糖体的结构和功能的研究”而获得年度的诺贝尔化学奖。3名获奖者通过独立的研究和科学实验，使用了X射线结晶学的方法得到了核糖体的三维结构，绘制出3D模型。在原子水平上分析了由几十万个原子构成的核糖体的结构和功能．扫清了目前抗生素研究中的许多障碍，并弄清了一些细菌的抗药机制。如今已被应用于开发新的抗生素，直接帮助挽救生命及减少人类的痛苦，也为科学探索提供了新工具。

结合材料，运用实践和认识关系的知识，说明三位科学家的科学实验过程。

在等差数列{a_n}中，a₂=1，a₄=5，则{a_n}的前5项和S₅=（　　）

We didn’t go home _____ we finished the work.