1.(2×2-1)/2，(3×3-1)/5，(4×4-1)/8，(5×5-1)/11，()
A.12/13
B.35/13
C.12/7
D.5/2
2.
A.1/6
B.1/8
C.1/4
D.1/9
3.1/6，2/3，3/2，8/3，()
A.10/3
B.25/6
C.5
D.35/6
4.1/4，3/10，()，2/5
A.23/50
B.17/40
C.11/30
D.7/20
5.
