Read the situation and frame meaningful sentences using the words in brackets.
When they left college, Mary and Sue started making films together. They still make films.
(make/ ten films together) They [fill-regular]
(make/ films since they left college) [fill-regular]

With the assistance of the hint, we are able to understand that the 2 girls have performed action ‘X’ within the past and are still performing it.
The first verb states an action that materialized and finished within the past itself. They started making films once they left college, hence we'll use the easy past to indicate the right sense of the sentence, that is; They made ten films together.

Now, the second action ‘they still make films’, states that they began making films within the past and still do so. Hence, we'll use the current perfect imperfect, that is; they need been making films since they left college.
The correct answer is Option A.

Note: We always use this Perfect continuous verb for an action that began within the past and continued within the present.