Final answer:
Contact Builder in Salesforce Marketing Cloud can alter data in Data Extensions through two methods: adding a single record to add/update contact information or clearing records to remove data for data hygiene or preparation for new data.
Step-by-step explanation:
Contact Builder is a tool within Salesforce Marketing Cloud that allows users to manage and interact with their contact data. There are two ways in which Contact Builder can alter the data in Data Extensions: by adding a single record or by clearing records from the Data Extension.
Add Single Record: Users can manually add individual records to a Data Extension in Contact Builder. This could be used to add a new contact manually or update details for an existing contact.
Clear Records from the Data Extension: This feature enables users to delete records from a Data Extension to maintain data hygiene or to prepare the Data Extension for new data to be imported or entered.
While options B (Reconcile contact data on multiple contact ID) and D (Export from Data Extension to FTP) are also activities that can occur within Salesforce Marketing Cloud, they do not directly alter the data in a Data Extension the way options A and C do.