As evidenced in theHayashi vs. Popovcase (Rest of the Story -- Barry Bonds 73rd home run baseball case):

a.Hiring an attorney on a contingency basis is wise when the outcome of the case is uncertain.

b.Hiring an attorney on a contingency basis is wise when the client is a defending a frivolous case.

c.Hiring an attorney on an hourly rate is wise when the outcome of the amount in dispute is certain.

d.Hiring an attorney on an hourly rate is wise when the outcome of the amount in dispute is uncertain.

e.A and C are correct.