In which of the following examples is the person likely to show the highest, and very steady, rate of response over time?

a. ?In hopes of winning a big jackpot, Penny plays the slot machines at a nearby casino.
b. ?Sam earns extra money by mowing his neighbors’ lawns in the summer and shoveling their driveways and sidewalks in the winter. He charges $20 per job.
c. ?Hoping to catch a message from her boyfriend, Wendy checks her e-mail again and again throughout the day.
d. ?Jaime has a paper due once a month in his sociology course. His productivity is low at the beginning of the month and high as the deadline approaches.

ANSWER:
a