Refer to the following series and answer the question (all numbers are single digit numbers only).
(Left) 4 2 1 5 7 9 8 7 3 4 3 5 6 2 1 5 1 5 2 8 5 6 9 7 4 7 3 (Right)
How many such odd digits are there each of which is immediately preceded by an odd digit and also immediately followed by an even digit?
A7
B6
C5
D4