Which of the following can be manipulated to format the day of the week in a date string?

The formatting of the day of the week in a date string can be achieved by using the code "%A." This format specifier is specifically designated to return the full name of the day, such as "Monday," "Tuesday," etc.

Each of the other format specifiers serves a different purpose: "%B" is used to represent the full name of the month (e.g., "January," "February"), "%C" provides the century (the year divided by 100), and "%D" returns the date in a more general format (often used as a shorthand for "mm/dd/yy"). None of these options allow for the manipulation or formatting specifically tied to the day of the week. Thus, "%A" is the correct choice to achieve the desired formatting for the day of the week in a date string.