Explain the mechanism by which sitelink extensions enhance ad visibility and user engagement.

Sitelink extensions enhance ad visibility and user engagement by providing additional links within the ad that direct users to specific pages on the advertiser's website. When sitelink extensions are displayed, the ad takes up more space on the search engine results page (SERP), making it more prominent and increasing the likelihood that users will notice it. Each sitelink extension includes a short description that provides context and entices users to click. These descriptions offer more information than the main ad copy, helping users understand the different options available on the website. Sitelink extensions also improve user engagement by providing users with more relevant choices. Instead of directing all users to the same landing page, sitelink extensions allow them to navigate directly to the specific information or product they are looking for. For example, an ad for a clothing store might include sitelinks for 'Men's Shirts', 'Women's Dresses', and 'Sale Items'. This allows users to quickly find the items they are interested in, improving their overall experience and increasing the likelihood of a conversion. By providing multiple entry points to the website, sitelink extensions also increase the chances that a user will find what they are looking for and make a purchase. The added visibility and improved user experience provided by sitelink extensions can lead to higher click-through rates (CTR) and increased conversion rates, ultimately improving the overall performance of the advertising campaign.