If it was just weight and upthrust or weight and drag, thn according to simple IGCSE Physics, I would answer B, as at constant(terminal) velocity the downward forces must equal the upward forces. But the case is different here, with three forces acting. I neither know which year this question is from, nor do I have any mark scheme for this one.
Are you sure about this Ari?
Drag (D) + Upthrust (U) = Weight (W)