The correct option is A Unequal distribution of auxins
The bending of the stem towards sunlight in plants is due to unequal distribution of auxin. Auxin hormone synthesized by meristematic cells at shoot tip moves from the tip of the stem and concentrates more on the side not receiving light or shady side. Due to the presence of more auxin hormones, the shady side of the stem grows faster than the side receiving light. As a result, the stem bends towards the direction of light.