didn't realise the spacing had changed to 8.33khz though from 25khz, when did this happen?
Several years ago but it was limited to ATC frequencies above FL200 so that only the airlines had to spend money to update their radios. Most GA stuff is still 25khz channel spacing though the Garmin 430/530 has an option in the menu to switch to 8.33khz.
CAP413 1.4.4 matches your answer B but I have rarely heard this followed in practise. Answer D is the normal response but technically it's the wrong answer. Perhaps you should contact the publishers?