Looking at it again this morning, I think:
a) 274 is correct for a fixed card RBI, at right angles to track, passing to the right of the NDB.
b) 284 is correct for a fixed card RBI if you are exactly West of the NDB, not at right angles to track.
c) 094 is correct for a fixed card RBI if you are passing to the left of the NDB, not to the right.
d) 084 is correct for a movable card RBI with the 170 track on top instead of the more sensible 166 heading that an RMI would have.
So I would still go with a), because it fits the question best.