Jack and Jill are married and file a joint return and they have reached full retirement age. They are working part time and earning $36,000 per year. Are their social security benefits taxable, and if so, what percent of their benefits are taxable?

A. Yes, up to 50% of their social security benefits are taxable.

B. No, their social security benefits are not taxable

C. Yes, all their social security benefits are taxable.

D. Yes, up to 85% of their social security benefits are taxable.