Which pronoun agrees with the antecedent in the sentence?

all of the paint is still in container.

a. their
b. theirs
c. its
d. it's

C.its
All of the paint is still in ___its container. 

we are asked to fill in the correct pronoun of the sentence with the missing element: All of the paint is still in _ container. The antecedent that is replaced by the supposed pronoun is all of the paint. All is referred to as a collective noun, hence singular. So the answer in this case should be C. its