The Above Figure Shows the Production Possibility Frontier for a Country

The above figure shows the production possibility frontier for a country. Suppose the country is producing at point D. What is the opportunity cost of increasing the production of rice to 15 tonnes?

A) 9 thousand bottles of wine
B) 12 tonnes of rice
C) 15 thousand bottles of wine
D) 6 thousand bottles of wine
E) Nothing, it is a free lunch.