Has nothing to do with T:W.
LIFT is a function of Indicated airspeed. At high IAS, it doesn't take much AoA to creat 1-g of lift.
At lower IAS, it takes MORE AoA to get 1-g of lift.
Do not confuse AoA with aircraft pitch. Yes, in general, as you climb, the pitch will lower.
The classic definition of AoA is "the angle between the mean chord-line and the relative wind." No one can imagine that.
But if I said "It's the difference between where your nose is pointed, and where your butt is going," it makes more sense.
(Works for yaw angle, too).
Note in your example, answers C and D are identical. Real answer to the question: in a constant Mach climb, TAS decreases, IAS decreases, AoA Increases.