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Use the table below to answer the following question.

Table $2\mathrm{.}2\mathrm{.}1$

$\backslash$table$[[\backslash$table$[[$Ethanol$],[($barrels per day$)]],,\backslash$table$[[$Food crops$],[($tonnes per day$)]]],[70,$and,$0],[64,$and,$1],[54,$and,$2],[40,$and,$3],[22,$and,$4],[0,$and,$5]]$

A country produces ethanol and food crops. Table $2\mathrm{.}2\mathrm{.}1$ shows the country's PPF$.$ The marginal benefit of food crops

a$.$ equals $70$ barrels of ethanol.

b$.$ remains constant as the quantity of food crops produced increases from $1$ tonne a day to $2$ tonnes a day.

c$.$ equals the marginal cost of food crops.

d$.$ increases as the quantity of food crops produced increases from $1$ tonne a day to $2$ tonnes a day.

e$.$ cannot be calculated from the table.