Explanation:

- Relentless means continuing without getting weaker; it shows no sign of stopping or letting up.

- Option 1: Tenacious describes someone who is very determined and doesn’t give up easily.

- Option 2: Determined means having made a firm decision and being resolved not to change it.

- Option 3: Yielding refers to someone or something that gives way under pressure; it easily bends or surrenders.

- Option 4: Swarming refers to moving in a large, dense group. It doesn’t connect with relentlessness.

- The correct antonym of relentless is Yielding as it implies giving in easily, which is the opposite of relentless.

Correct Answer: Option 3 - Yielding