Makayla has designed a new type of gearshift to be used in automobiles with an automatic transmission. Before she proposes it to the major car manufacturers, she wants to make sure it will be more advantageous for people who drive such cars. With which of the following types of psychologist would Makayla most want to consult about her design?

a. human-factors psychologist

b. environmental psychologist

c. industrial/organizational psychologist

d. machinery psychologist