Explanation
Triggering an automation via API is a method that allows marketers to start an automation based on an external event or process, such as a website action. The automation can be triggered by calling the Perform method of the Automation object in the SOAP API. This method can be used to run an automation immediately or schedule it for a future date and time.

Explanation
Ensuring preferred channel is available in subscriber data is the correct answer. This option allows you to use dynamic content or decision splits in Journey Builder to honor the opt-in communication method of your subscribers. For example, you can use an attribute or a data extension field that indicates whether a subscriber opted-in via email or SMS, and then use that information to send them a welcome message through their preferred channel. Sending both email and SMS to ensure subscribers get NTO's messages is not a good option, as it may annoy or spam your subscribers who only opted-in for one channel. Creating one entry source for each messaging channel is not necessary, as you can use one entry source that supports both channels, such as API event or CloudPages form submit. You can learn more about this in the [Journey Builder Basics] module on Trailhead.