Don't need thorough explanation, just the answer

The real interest rate is related to the supply of loanable funds because O a. positively; people are motivated to increase their consumption expenditure as the real interest rate rises O b. negatively; the opportunity cost of consumption expenditure increases as the real interest rate rises O c. positively; the opportunity cost of consumption expenditure increases as the real interest rate rises O d. negatively; people are motivated to save more as the real interest rate rises