The distance from Y to Z is thrice that from X to Y. Two trains A and B travel from X to Z via Y The speed of train B is double that of train A while traveling from X to Y and their speeds are interchanged while traveling from Y to Z. The ratio of the time taken by train A to that taken by train B in traveling from X to Z is?

A

5:7

B

8:7

C

7:9

D

3:5

E

4:9