To optimize their campaign, an advertiser wants to reach new people who behave similarly to one of their existing audiences. What should they do?

The selected answer is correct because an actalike audience is Pinterest’s specific tool for prospecting, designed to identify and target new users who share similar behaviors, interests, and engagement patterns with a source audience, such as a customer list or website visitors. While "expanding targeting" or "adding keywords" can increase reach, those methods rely on broad parameters or specific terms rather than the sophisticated algorithmic modeling used to build an actalike audience, which leverages Pinterest's unique data to find the "lookalikes" most likely to find the advertiser's content relevant and actionable.