A Custom Audience is the correct choice for retargeting because it allows a business to create an audience list from its own sources. To target people who have previously purchased an item, the business would use the Meta Pixel on its website to track the "Purchase" standard event. This data is then used to build a Custom Audience of those specific users. This method enables precise retargeting based on past interactions with the business's own assets, directly fulfilling the requirement of the question.

B. Lookalike Audience: This is used for prospecting, not retargeting. It finds new people who share similar characteristics with an existing source audience (like past purchasers) to expand reach.

C. Page followers: This targets people who follow the business's Facebook Page. This audience is not specific to users who have made a purchase on the website.

D. Behaviors: This targeting option uses Meta's data on user activities across platforms. It cannot be used to specifically target people who purchased from your particular website.

1. Meta Business Help Center, "About Custom Audiences." This official documentation states, "A Custom Audience is an ad targeting option that lets you find your existing audiences among people who are on Facebook... You can use sources like customer lists, website or app traffic, or engagement on Facebook, to create Custom Audiences of people who already know your business." This directly supports using website traffic (purchases) for retargeting.

Source: Meta Business Help Center, Article ID: aBuwxLp1L5D.

2. Meta Business Help Center, "About website Custom Audiences." This source specifies the mechanism for the scenario: "You can create a website Custom Audience of people who have visited your website or taken specific actions there using the Meta Pixel... For example, you can show ads to people who have visited your website in the past 30 days or people who have taken a specific action, like making a purchase."

Source: Meta Business Help Center, Article ID: aBuzx8w1Y5D.

3. Meta Business Help Center, "About Lookalike Audiences." This document clarifies the purpose of Lookalike Audiences, distinguishing them from retargeting tools: "When you create a Lookalike Audience, you choose a source audience... We then identify the common qualities of the people in it... and find similar people. It's a way to reach new people who are likely to be interested in your business because they're similar to your best existing customers."

Source: Meta Business Help Center, Article ID: aBuwLp1L5D.