Final answer:
In a production environment, the end-user is commonly responsible for the source of data input, as they are the ones entering data into the application that processes and stores it.
Step-by-step explanation:
In a production environment, the user responsible for the source of data input is typically the C. End-User. The end-user interacts with the application interface to enter data that is processed by the application and ultimately stored in the database. They play a critical role in the data lifecycle as they initiate the creation or updating of data. It's important for developers and administrators to ensure that the user interface is intuitive and secure to facilitate accurate and efficient data input by end-users.