推广活动 A 的目标是提高网站访问量。对于此类推广活动，以下哪项指标最具参考价值？

For campaigns aimed at increasing website traffic, Click-Through Rate (CTR) is the most valuable metric because it directly measures the percentage of people who saw your ad and then clicked on it to visit your website. A high CTR indicates that your ad creative and targeting are effective in driving users to your site. Follower growth is more relevant for brand awareness or community building, not direct traffic. Reach and impressions measure how many people saw your ad and how many times it was shown, respectively, but they don't indicate whether users actually took the desired action of visiting your website.