You are considering investing in several comparable 10-year 5% semi annual coupon bonds priced. The make whole call provisions of the bonds are listed below. Assuming all 5 bonds are using the same benchmark treasury bond, select which make whole call provision terms below provide for the lowest call risk.

a. Make whole at 15bps until maturity, bond currently trading at 100bp spread over benchmark.

b. Make whole at 20bps until maturity, bond currently trading at 100bp spread over benchmark.

c. Make whole at 15bps until maturity, bond currently trading at 200bp spread over benchmark.

d. Make whole at 20bps until maturity, bond currently trading at 200bp spread over benchmark.