5. A bag contains 7 red marbles and 5 yellow marbles. From the bag, 3 marbles are taken randomly at once. How many ways exist if all 3 taken marbles are the red ones?
A. 35
B. 105
C. 220
D. 360
E. 480

Is the answer just simply C(7,3)? Please give me some explanations.Thanks in advance.