Of the Following, Which Would Be Most Likely to Increase

Of the following, which would be most likely to increase direct performance on the job the most?

A) a promotion based on seniority.
B) three weeks of paid vacation tied to a person's time on the job.
C) everyone gets a turkey for Christmas.
D) a salesperson's commission tied directly to the amount of sales s/he achieves.
E) the supervisor says "good morning" to a person each morning at 8 a.m.