If a cobbler buys leather for Rs100 and thread for Rs50 and uses them to produce and sell Rs500 worth of shoes to consumers the contribution to GDP is ?

A. the value placed on the last unit of production by buyers exceeds the cost of production
B. the cost of production on the last unit produced exceeds the value placed on it by buyers.
C. consumer surplus is maximized
D. total surplus is maximized
E. producer surplus is maximized