20/9 5/51 10/51 17/51
A15/15 B16/51 C26/51 D37/51
选c
题目有错,第一项应该是2/51
2/51 5/51 10/51 17/51 (26/51)
分子2,5,10,17,26前一项依次加3,5,7,9得后一项,
3,5,7,9是公差为2 的等差数列。