The correct option is D 3
At first glance while looking at the expression 4a4−2(3+a4−ab+4b3)−2a4, degree seems to be 4. But on simplification,
4a4−2(3+a4−ab+4b3)−2a4
=4a4−6−2a4+2ab−8b3−2a4
=2ab−8b3−6
3 would be the degree of this polynomial which is obtained from 2nd term.