The correct answer is option B, The spread of the roots around the plants is usually greater than the depth
The growth of the roots in the plant is not directed towards any nutrients or resource. Alternatively the growth of roots is diverted towards the availability of oxygen. Since the availability of oxygen decreases exponentially with the depth below the surface of soil, the root growth is dampened after a certain depth in the soil. Also factors like clay content, resistance to penetration also restricts the root growth downward. These restricting factors are not available in the horizontal direction of growth of roots. Thus roots grow more laterally than vertically.