The purchasing agent of an organization acquired some raw materials at a bargain price, even though she knew that their quality was lower than that of the materials customarily used. This action resulted in a favorable raw materials purchase price variance that might very well have been more than offset by:

a. an unfavorable raw materials usage variance

b. a favorable direct labor efficiency variance

c. an unfavorable variable overhead spending variance.

d. an unfavorable direct labor rate variance

Why?