Final answer:
The GTO (Golgi tendon organ) responds to changes in tension in the muscle and helps to relax the muscle when tension reaches a certain threshold.
Step-by-step explanation:
The GTO (Golgi tendon organ) is an organ found in tendons that responds to changes in tension, or force, in the muscle. When the tension in the muscle reaches a certain threshold, the GTO sends signals to inhibit the muscle activity, causing it to relax. Therefore, the correct answer to your question is option D) Relax.