Question 5: Her brother is ______ soccer player on his team.
This is the superlative structure (because in the sentence there is a comparative object (Her brother) to be compared with a group (his team)).
We have class A (grammatical error, do not use “the” in the superlative), type B (because this is the comparative form), type C (wrong form of the adjective in the superlative).
So the correct answer is D (the best)
Translation: Her brother is the best scorer on the team.