Coastal plains and Interior plains is in elevation. Coastal plains have low elevation and low relief. Interior plains have varied elevation and low relief. Coastal plains also lie along the shore while Interior plains are surrounded by other hopefully this helps
I believe it's b but I may be wrong
Grain farming is done for economic activity and this makes it commercial. It is highly specialized and mechanised. The yield per acre is low so the farms are big. The yield is high per man so little manpower is needed for production. Grain farming is subject to market conditions like climate.