The depth of rice root zone, is A. 50 cm B. 60 cm C. 80 cm D. 90 cm

The correct answer is B. 60 cm.

Rice is a semiaquatic plant that grows in flooded soils. The roots of rice plants are able to grow in waterlogged soils because they have aerenchyma, which are air-filled spaces in the roots that allow them to take up oxygen. The depth of the rice root zone varies depending on the variety of rice and the soil conditions. However, most rice plants have roots that grow to a depth of 60 cm.

Option A is incorrect because the depth of the rice root zone is typically greater than 50 cm. Option C is incorrect because the depth of the rice root zone is typically less than 80 cm. Option D is incorrect because the depth of the rice root zone is typically less than 90 cm.