Which of the following would be a likely explanation for a favorable direct material variance?

a) Direct laborers were less overtime hours than expected.

b) The direct material used to produce each unit was higher than anticipated.

c) A machine that processes the direct material missed its scheduled maintenance and did not operate as efficiently as expected.

d) The purchase price of direct materials used in production were less than expected.

e) The wage rate demanded by the market was lower per hour than the estimated wage rate.