Number of permutations of `1,2,3,4,5,6,7,8`, and `9` taken all at a time are such that digit `1` appearing somewhere to the left of `2` and digit `3` appearing to the left of `4` and digit `5` somewhere to the left of `6`, is
(e.g. `815723946` would be one such permutation)
A. `9.7!`
B. `8!`
C. `5!4!`
D. `8!4!`