Concept:The Grey Revolution refers to the increased use of chemical fertilizers to boost agricultural productivity.Explanation:This revolution focused on applying fertilizers like urea and superphosphate to improve soil fertility.It supported the Green Revolution by enhancing crop yields and helping India achieve food self-sufficiency in the 1960s-70s.Thus, the Grey Revolution is directly linked to fertilizers, not fisheries, oilseeds, or potatoes.Answer:B. Fertilizers