Semaphores: How many A's and B's are printed from the following processes:

Can someone please explain to me how this is calculated? I'm confused about how semaphores work when they aren't implemented as mutex locks. I think the answer is B.), but i'm not sure why that is. Thanks.

17. As shown with the following code, four processes produce output using the routine "printf" and synchronize using three semaphores "R", "S" and "T." 25 Semaphore R=1, S = 3, T = 0; /* initialization */ /*process 1 *//* process 2/ while (true) /*process 3 while (true) P (T) /*process 4 while (true) ( */ while (true) [ P (S) printf('A') P (T) printf ('B'); printf ('C' V (T) P (R); printf 'E'; V (T) printf ('D' V (R) 17.1 How many A and B's are printed when this set of processes runs? A. 2 As and 3 B B. 3 As and any Bs C. 1A and 0 B D. Any As and any Bs