The correct option is D px orbital of A and s orbital of B
p-orbitals are directional in nature. So, only px orbitals can take part in overlapping if bond is formed along x-axis.
However, s-orbital, being non-directional (spherical), overlaps in all the directions.
So, only px and s orbitals overlapping is favourable for the formation of sigma bond along x-axis.
(px of A and s of B)