I would say that the answer is C, since variations in crop restore the nitrogen in the soil from certain bacteria growing on the root of beans, including legumes.
Alternate their normal crops with crops of legumes.
Explanation:
Certain plants, known as nitrogen fixing plants, can draw nitrogen from the air and store it in their roots. They do so through a bacteria called rhizobium. This bacteria infects legume plants in particular, and converts nitrogen gas to store it in the roots of these plants. In this way, a farmer could increase the amount of naturally occurring nitrate in his farm field.
Auditory deals with the sense of hearing and all of the choices start with a different external factor end in a logical response, however, B is the answer because it’s external factor, a siren, is the only one that involves the sense of hearing.
