The correct answer to this question isVmax decreases, KM is unchanged. Vmax is a reaction rate. This rate occurs when a substrate fully saturates an enzyme. When this saturation occurs, it indicates that all of the binding sites are occupied constantly. KM is the measure of the enzyme's affinity substrate.
For example, if an enzyme has a high KM, it will have a low substrate. If it has a low KM, it will have a high substrate. Both Vmax and KM are parameters. They are important because they define an enzyme's kinetic behavior. This type of question would be found on a biology test.