How does flooding rice fields reduce the need for herbicides and pesticides in rice farming?
a. while rice has a submerged growth state, most weeds and pests do not.
b. flooding the fields causes thesoil to degrade so weeds cannot take root.
c. residual herbicides and pesticides from previous seasons dissolve in the water.
d. all of the above?

The rice fields are flooded in order to prevent the growth of the weeds and the attack of the pests. The flooding overcomes the need to use herbicides and pesticides on the rice crops. The rice plants survive and grow in the flooded fields as they have the submerged growth state, but most of the weeds and the pests cannot survive in such conditions. This protects the rice crops from the harmful effects of the weeds and pests on their growth.

Hence, the answer is option (a).