In the figure below, the loanable funds market is in equilibrium at A with the interest rate $I{R}_1.$ In conducting monetary policy, the Federal Reserve engages in the buying of US Treasury securities on the open market, which causes

a$.$ both the demand for loanable funds and the supply of loanable funds to increase to $D^{\text{'}}$ and $S^{\text{'}}$ respectively, keeping the equilibrium interest rate at IR $I_1.$

b$.$ the supply of loanable funds to increase to $S^{\text{'}},$ causing the equilibrium interest rate to fall to $I{R}_3.$

c$.$ the demand for loanable funds to increase to $D^{\text{'}},$ causing the equilibrium interest rate to increase to $I{R}_2.$

d$.$ no change in the loanable funds market, so the equilibrium interest rate remains at $I{R}_1.$