It would be D...
If the resistance increases it leaves u with two options...B & D cuz N moves towards Y...larger length of the wire
If galvanometer has to have a zero deflection(minimum deflection), it means V(p.d)=IR will decrease
that is becuz Resistance is high...so Voltage decreases if current is very low
This is what I think.,...maybe some other reason...but from the basic knowledge i think this is what it is....astar may further clarify it