Why does sucrase not hydrolyse lactose?

"because the reaction is to slow to make an effect, if a enzyme is added then it can hydrolyse lactose but it can take more than 6 years without the addition of an enzyme" Is bull the real answer is because the active site of the two substances are different and so the sucrase becasue Lactose has a different shape/structure which does not fit/bind to active site of enzyme/sucrase.