You may have chosen this answer because there are zeros in all three equations. However, $\displaystyle{{b}}^{{y}}={x}\usepackage{cmbright}\Huge\$ is equivalent to $\displaystyle{\log}_{{{b}}}{x}={y}\usepackage{cmbright}\Huge\$ . This means that $\displaystyle{y}={0}\usepackage{cmbright}\Huge\$ when the exponent is 0. The correct answer is I and III.