Walter pays interest expense of $2,500 to acquire his investment portfolio during the current year. Walter receives $2,000 in interest from investments in General Motors and Xerox bonds and $6,000 in interest from investments in City of San Francisco bonds. How much of Walter's interest expense is NOT deductible?

a. $ 625

b. None of the above.

c. $ 1,875

d. $2,500

e. $ 0