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

a$.$ 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

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

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

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