To ensure a form supports accessibility, especially when enabling a user to specify a date, using an interface that is intuitive and easy to navigate is key. Among the provided options, a calendar control that displays an entire month is the most accessible and user-friendly method for date selection.

C. Use a calendar control that displays an entire month: This method provides a visual and interactive way for users to select a date, offering both keyboard navigation and screen reader support, making it accessible to users with a wide range of disabilities, including visual impairments. A month view gives users an overview of the dates, allowing for easy selection without requiring manual date entry, which can be prone to errors and less accessible for some users.

Configuring a text box for date entry (A) may not be as accessible because it relies on users correctly typing the date, which can be challenging for some people. Using a calendar control that displays an entire year (B) can be overwhelming and less practical for date selection. Providing separate controls for month, day, and year (D) could increase complexity and potentially decrease accessibility due to the need to navigate between multiple controls.