Greta describes herself as someone who gets things “stuck in my head,” especially if it worries her. Based on this text, Greta shows this in her activism by being

The correct answer is C) relentless.

Greta’s description of getting things “stuck in my head,” particularly worries, indicates that she is persistent and determined about issues that concern her. This relentless pursuit reflects her commitment to activism, as she continuously brings attention to causes that matter to her.