Which of the following interest expense amounts is not deductible in the current year?

a. Education loan interest of $2,000, assuming the taxpayer has income of $30,000.

b. Home equity loan interest of $6,000, on a loan of $90,000, the proceeds of which were used to add a new bedroom and bathroom to an existing primary residence.

c. Investment interest expense of $1,200, assuming the taxpayer has no investment income.

d. Qualified residence interest of $70,000 on a $730,000 loan used to purchase a luxury apartment in downtown San Diego.