Because of how the brain learns, if a person rather did four sets of a

Question: Because of how the brain learns, if a person rather did four sets of an exercise over five days than doing 20 sets in one day, it might be a way to improve technique or form even if the person doesn’t add additional weight.

All the answer choices consist of 2 clauses and the second clause has the same format (it might / will be a way to improve). Hence, let's focus on the first clause.
The splits are:

1. Comparison form - There are 4 forms exist and
rather X than Y
X than Y
rather X rather than Y
X rather than Y
From all these options, X rather than Y is preferred. The others are either redundant or non-idiomatic

2. Verb tense
Since the sentence is portraying facts, simple present should be used instead of simple past.

A. if a person rather did four sets of an exercise over five days than doing 20 sets in one day, it might be a way to improve
The correct comparison should be If a person does X rather than Y, it might be a way to improve
Also, present tense should be used instead of simple past

B. if a person did four sets of an exercise over five days than doing 20 sets in one day, it might be a way to improve
Verb tense issue - Same like A

C. if a person rather did four sets of an exercise over five days rather than they do 20 sets in one day, it will be a way to improve
Verb tense issue - same like A

D. if a person does four sets of an exercise over five days rather than 20 sets in one day, it might be a way to improve
Correct

E. a person might rather do four sets of an exercise over five days than doing 20 sets in one day, it might be a way to improve
Simple present should be used instead of future tense.