Concept:Rain water becomes available to crops only after it enters the plant through the roots.Explanation:When rain falls, it soaks into the soil and becomes part of the soil water.Crops take up this water through their root hairs.Root hairs have thin, permeable walls that contain cellulose and pectic substances.These substances are strongly hydrophilic, meaning they attract and absorb water easily.This process of taking in water from the soil through the roots is called root absorption.Answer:D. root absorbtion