두개 문제중 답이 뭘까요?

a, b 인가요?

3번은 불가산, 4번은 가산인가요?
뜻 차이를 모르겠어요..

3. The reunion band concert was so popular
that the stadium was filled to ( )
a. capacity
b. capacities
c. a capacity
d. all capacities

4. A few universal serial buses even have ( )
of 10 G-bytes, which is similar to that of hard
drives.
a. a capacity
b. the capacity
c. any capacity
d. each capacity