What is the level of output every firm strives for?

a) when fixed and marginal cost are equal
b) when variable cost and marginal cost rise at the same time
c) when marginal revenue equals marginal cost
d) when marginal revenue is greater than marginal cost

The details about the statues, i believe, are that they're carved from blocks of igneous stone, many of them are partially buried under the ground which to preserve and protect them from the harsh environment on easter island, and many of the facial features have washed away. also, the most well-preserved one is at the british museum in london.these are just guesses from what i can see and what i think i read correctly. i'm sorry i couldn't be more .