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 $10,000, 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