The diagram below shows the market for a key agricultural crop. The government decides to intervene by introducing a minimum price (price floor) at P1 P_1\,P1 to support domestic farmers. Under this scheme, the government commits to buying up any resulting surplus at this minimum price.

Which area represents the total cost to the taxpayer of purchasing this market surplus?
Area OP1AMOP_1AMOP1AM
Area OP1BNOP_1BNOP1BN
Area MABNMABNMABN
Area ABNABNABN