Answer:
The sentence that shows correct use of subordination is:
A. While Tom sanded the floors in the living room, Meg painted the kitchen walls.
Explanation:
Even though the sentences look very similar at first, we need to pay attention to details to find the correct one.
The subordinate clause in the sentence is "while Tom sanded the floors in the living room." This clause begins with the subordinating conjunction "while", establishing a relationship of time with the main clause.
If we begin the sentence with the subordinate clause, then we should use a comma right after it to separate it from the main clause. This is what makes letter A correct and letter D incorrect.
If the main clause is the first one in the sentence, there is no need for a comma to separate it from the subordinate clause. This is what makes letter B incorrect.
Letter C is incorrect due to the use of "until", which is unnecessary since we already have "while" in the sentence.