Research on Willpower Has Demonstrated That

Research on willpower has demonstrated that

A) the stronger one's willpower, the less glucose is needed to sustain it.
B) when willpower is used to achieve a goal, one will have less willpower immediately available to achieve a later goal.
C) willpower is an unlimited resource that can be used to accomplish any task.
D) if one exerts willpower regularly, it's important to reduce one's glucose levels.