If aA perfectly competitive firm maximizes profits or minimizes losses in the short$-$run by producing at the output level at which:

a$.$ marginal revenue equals marginal cost.

b$.$ total revenue equals total cost.

c$.$ total revenue is at a maximum.

d$.$ none of the above. perfectly competitive firm sells $10$ units of output at a market price of $$5$ per unit, its marginal revenue per unit is:

a$.$ $$5.$

b$.$ $$50.$

c$.$ more than $$5$ but less than $$50.$

d$.$ less than $$5.$