假设某大肠杆菌含¹⁴N的DNA的相对分子质量为a，若将其长期培养在含¹⁵N的培养基中便得到含¹⁵N的DNA，相对分子质量为b。现将含¹⁵N的DNA大肠杆菌再培养在¹⁴N的培养基中，子二代DNA的相对分子质量平均为（   ）

根据短文理解，完成下列各题。

    This is our school. There is a very nice 1 in our school. It is big and bright（明亮的）. It has all 2 of books and newspapers in it. We can 3story books, picture books, English books and many 4 books there. We can 5 do some reading there. Maria likes reading very much. She goes to the library every day. Look, she 6 and reading by the window (窗口). Li Ming 7 borrows some books and reads them in it. He likes books.

    I'm going to borrow an 8 story book. Our English teacher often 9 us to do more speaking and reading. I like English very much. I 10 I can do well in English. What about your school?

法国大革命高举反封建专制的旗帜，震撼了整个欧洲大陆的封建秩序。如图所示人物把法国大革命推向高潮的是（　　）

投掷两颗质地均匀的骰子，则向上的点数之积为6的概率等于（　　）