Correct Answer: Yielding

Solution : The correct choice is the third option.

Explanation: "Relentless" means unyielding in pursuit or action. Its opposite, "yielding" denotes being flexible, giving in, or easily surrendering, which contrasts with the persistent nature of being relentless.

The meanings of the other options are as follows:

• Tenacious refers to holding firmly and being persistent in maintaining or adhering to something.
• Determined refers to having a firm purpose and being resolute in achieving a goal.
• Swarming refers to gathering or moving in large numbers.

Therefore, the correct answer is yielding.