Economies of scale is a situation in which firm experiences the
cost advantage such that with the increasing level of production
the cost decreases and it implies that the average cost curve will
be download sloping in the long run. So the right answer is option
B, that is, the use of larger; more specialized machines, because
when the firm uses larger and more specialised machines it implies
that the firm can produce more of the output due to the better and
specialised machine which also helps in increasing the productivity
of the workers.