Six new graduates are hired by an engineering firm. Each is assigned at random to one of six cubicles arranged in a row in the back of the room that houses the engineering staff. Two of the graduates are Bill and Cathy. What is the probability that they are assigned adjacent cubicles? (Round the final answer to three decimal places.)
a. 0.333
b. 0.167
c. 0.500
d. 0.833