Figure 1 shows two demand (D1 D_1\,D1 and D2D_2D2) curves and two supply (S1 S_1\,S1 and S2S_2S2) curves in the market for butter. Butter and margarine are substitutes. All other things being equal, which one of the following is the most likely explanation of the move from E1 E_1\,E1 to E2 E_2\,E2 in the market for butter?
A fall in the price of butter and a rise in productivity in margarine production
An increase in a government subsidy to dairy farmers and a rise in the price of margarine
An increase in the price of margarine and a fall in the cost of milk used to make butter
The introduction of a tax on dairy farmers and a fall in the price of margarine
