Kristen has a difficult time retrieving the answers to simple multiplication problems from memory, causing her to spend a great deal of time on each word problem she encounters on tests. According to the limited-resource model, Kristen has trouble on math exams because

a. her poor math fact retrieval taxes her cognitive resources to the point of usurping energy from other processes.
b. she has limited knowledge of and experience with solving mathematical word problems.
c. she has limited knowledge of and experience with problem solving that requires memory resources.
d. numerical information does not flow through the proper memory sequence for Kristen to successfully solve math problems.

A