I think the correct answer would be D. The specialized structure that helps a vascular plant to soak up water after a rainfall in a desert would be the extensive shallow root system with root hairs. An example of this would be the cactus. It has a root system that is very different from any plant that is not found in the desert. The roots are found just exactly below the surface. It is ready anytime to suck up water from rain or snowfall and transport it to the stem of the plant. Also, after a rain, the cactus would grow tiny roots in its body to aid in the absorption of water more quickly.
