Ballston-MU Station
Foggy Bottom-GWU Station
Please solve the multiple choice problem and put your answer (one of ABCD) in one "\boxed{}". According to the subway map, how many intermediate stops are there between Ballston-MU Station and Foggy Bottom-GWU Station (except for this two stops)? 
A) 21 
B) 19 
C) 17 
D) 4 
