Soil is like a factory for billions of living things, including insects, protozoa, and bacteria. These living things are working all the time, helping to create healthy soil for growing plants. Insects stir up soil so water and air can enter. Protozoa are tiny organisms that feed on bacteria in soil and release nutrients that plants can use. Bacteria help break down dead plant material.

Based on the context, what does the simile in the first sentence suggest about soil?

A. Soil requires the work of many living things to keep it healthy.
B. Small factories are set up in the soil by various living creatures.
C. Healthy plants require nutrient-rich soil created in factories.
D. Living things in the soil need nutrients in order to play their part.