Your vocal cords are located in your larynx also known as your vocal box. (The answer is A.)
It is true that according to the principle of overload, endurance is increased when muscles work for a longer period of time than usual.
The correct answer is "exercise"
By meaning, reinforcement means to make something stronger. In the context of relationship it means strong and deep human relationships.
Thus, reinforcement is an exercise in the relationship.
