If monetary policy does not cause a change in interest rates,

a- it can still affect the output gap and the inflation rate through the bank lending channel.

b- it can still affect the output gap and the inflation rate by the willingness and ability of the banks to make loans.

c- it cannot affect the output gap and the inflation rate because the effect of the monetary policy depends on the change in interest rate.

d- both (a) and (b).

which one?