William and Helen are a common law couple who contribute regularly to their RRSPs. William's annual contribution limit is $10,000, while Helen has a limit of $4,000. William will have a higher marginal rate than Helen in retirement in 10 years' time. If William contributes $10,000 to Helen's RRSP, what benefit will the couple realize?

a. The benefit will be realized in retirement because withdrawals will be taxed at Helen's lower marginal tax rate.

b. William can make anadditional$10,000 contribution to his own RRSP in the current year.

c. If Helen withdraws the $10,000 next year, it will be taxed at her lower marginal rate.

d. A & B.