濒临两个海域，我国重要的兼产花生、冬小麦、棉花、温带水果和煤、石油的省是

阅读以上短文，完成下面各题，每空一词。

（A）

    My ideal schoo lis not far from my home. It takes me 15 minutes to walk there. In the school, there are a lot of trees and flowers. It's very beautiful. We also have a big school library, a swimming pool and seven computer rooms. We begin our classes at 8:00 a.m. and finish them at 4:00 p.m. So we have a lot of time for after-school activities. Every day we only do our homework for an hour. Every month we can go on a school trip. How wonderful the school life is!

$\frac{1}{3}$  + $\frac{2}{3}$  =1

$\frac{7}{3}$  + $\frac{8}{3}$  + $\frac{10}{3}$  + $\frac{11}{3}$  =12

$\frac{16}{3}+\frac{17}{3}+\frac{19}{3}+\frac{20}{3}+\frac{22}{3}+\frac{23}{3}$ =39

…

则当m＜n且m，n∈N时， $\frac{3m+1}{3}+\frac{3m+2}{3}+\frac{3m+4}{3}+\frac{3m+5}{3}+\cdots +\frac{3n-2}{3}+\frac{3n-1}{3}$ =____（最后结果用m，n表示）