The correct answer is B. per tonne.
A tonne is a unit of mass equal to 1,000 kilograms or 2,204.62262185 pounds. It is the international standard unit of measurement for mass and is used in many industries, including the sugar industry.
The cost unit of a sugar industry is the unit of measurement used to calculate the cost of producing sugar. The most common cost unit is the tonne, which is equal to 1,000 kilograms. The cost per tonne of sugar can vary depending on a number of factors, including the type of sugar produced, the location of the sugar mill, and the market conditions.
The other options are not correct because they are not units of mass. A litre is a unit of volume, an acre is a unit of land area, and a metre is a unit of length.