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

A. 9.7!
B. 8!
C. 5!4!
D. 8!4!