M and N are non-zero natural numbers. If M-N = 1, then the greatest common factor of M and N is

M and N are non-zero natural numbers. If M-N = 1, then the greatest common factor of M and N is

Think like this:
1. Because, M-N = 1, that is to say, m and N are two adjacent non-zero natural numbers
2. Then, the greatest common factor of two adjacent non-zero natural numbers is 1. The least common multiple is their product (MN)