What is the limit of social posting connectors you can create in your Pardot account?

An Administrator wants to make a list of all prospects who complete the Contact Us form but only wants them to be added the first time they complete the form. If a prospect is ever removed from the list, they shouldn't be able to get added back to it.
What is a recommended way to create this type of list?

What must happen in order for a newly created lead record in Salesforce to be created in Pardot immediately? (Choose two answers.)