The optimum depth of kor watering for a rice crop is 17.5 cm. This is because rice plants have a shallow root system and need to be watered frequently to prevent the soil from drying out. If the soil dries out, the rice plants will wilt and die. However, if the soil is too wet, the rice plants will be susceptible to diseases and pests. Therefore, it is important to water rice crops at the correct depth to ensure their health and productivity.
Option A (23.0 cm) is too deep. This will cause the rice plants to develop a deep root system, which is not necessary for their growth. In fact, a deep root system can make the rice plants more susceptible to diseases and pests.
Option B (19.0 cm) is too shallow. This will not provide the rice plants with enough water, and they will wilt and die.
Option C (17.5 cm) is the correct depth. This will provide the rice plants with enough water without causing them to develop a deep root system.
Option D (13.5 cm) is too shallow. This will not provide the rice plants with enough water, and they will wilt and die.