To effectively evaluate the performance of your ads and other marketing strategies, the most relevant option among those provided is:
C. Asking customers how they found out about your company or product.
This approach allows you to gather direct feedback on the effectiveness of your advertising and marketing efforts by understanding which channels are driving awareness and interest.
Options A, B, and D are not as effective in evaluating performance. Asking competitors may not yield honest or useful insights, collecting secondary data might inform you about the market but doesn't directly measure the performance of your current strategies, and sending out multiple press releases is more about outreach than evaluation.