According to Newton's second law
Vertical to the inclined plane: mgcosθ-N=masinθ.
Parallel to the inclined plane direction: f-mgsinθ=macosθ.
Get: N=mgcosθ-masinθ。
f=mgsinθ+macosθ
It can be seen that when the acceleration a increases, the supporting force n decreases and the friction force f increases. According to Newton's third law, the pressure of B on A gradually decreases, and the friction of B on A gradually increases.
So choose d