Evan Knows His GPA Would Skyrocket If He Could Break

Evan knows his GPA would skyrocket if he could break his horrible habit of procrastinating.An example of a commitment device Evan could use would be:

A) to allow himself one hour of leisure for every half-hour of studying he does each day.
B) to exercise before studying in order to be refreshed.
C) to pay a student to meet him each afternoon for 2 hours in the library to ensure he studies every day.
D) All of these are commitment devices.