Which key levers must clients invest in to strengthen user trust?

The correct answer is Security, transparency, control, and usefulness. These four pillars are essential for building and maintaining user trust. Security protects user data from breaches and misuse. Transparency informs users about data collection and usage practices. Control empowers users to manage their data and privacy settings. Usefulness ensures that data collection provides a clear benefit to the user, making the exchange worthwhile. Let's look at why the other options are incorrect: "Cross-site identifiers" are often seen as privacy-invasive and can erode trust, not strengthen it. "Data collection" itself isn't a lever for trust; rather, how data is collected and used (transparently, securely, with control) builds trust.