The correct answer is: Immediacy of reward following results

Rationale: Clarifying intended results, giving feedback on actual results and consistency of reward for results are essential for an individual to work out how much effort will be required, and whether it will be worth it for the rewards expected (due to consistency) to be available.

However, 'immediacy' is not necessarily required: people may have a high tolerance for 'delayed gratification', and be willing to wait for rewards as long as they have a reasonable expectation that they will eventually accrue. (As a student, for example, you may be working sacrificially hard now, in order to gain qualifications that will benefit your career in several years' time.)