Explanation: Data Extension, Audience Studio, API Event, Date Based Event are entry source types for Journey Builder. Entry source types are types of events or data sources that can trigger contacts to enter a journey in Journey Builder. Data Extension is an entry source type that allows contacts from a data extension to enter a journey based on a schedule or an automation. Audience Studio is an entry source type that allows contacts from Audience Studio segments to enter a journey based on a schedule or an automation. API Event is an entry source type that allows contacts to enter a journey based on an API call from an external system or application. Date Based Event is an entry source type that allows contacts from a data extension to enter a journey based on a date field in the data extension, such as birthday or anniversary.