Final answer:
A full deflection of the CDI when passing abeam a VOR indicates that the aircraft has passed 90 degrees to the selected radial, especially when the TO/FROM flag isn't functioning.
Step-by-step explanation:
When you pass abeam a VOR and the Course Deviation Indicator (CDI) shows a full deflection but the TO/FROM flag isn't working, it indicates that you have passed 90 degrees to the selected radial. What this means is that your aircraft is currently perpendicular to the course you have set on the VOR receiver. Deflection of the CDI needle to its full extent suggests that the selected VOR radial is either to the extreme left or right of your current position. In normal operation, the TO/FROM flag assists pilots in determining whether they are headed towards (TO) or away from (FROM) the station, but if it's inoperative, the position in relation to the radial is obtained solely from the CDI needle position.
It is important to note that a full deflection could also mean that the signal is not being received correctly—whether due to equipment failure, station being out of service, or being too far from the station. However, in this scenario, because only the TO/FROM flag is not working, the most likely answer is C) You have passed 90 degrees to the selected radial.