Four of the following five are alike in a certain way based on the given arrangement and thus form a group. Which is the one that does not belong to that group?

Study the following information carefully and answer the question given below: There are eight people A, B, C, D, M, N, O and P are living in a 8 floor Building on different floors from top to bottom (such as ground floor is numbered as 1 and top floor is numbered as 8) but not necessarily in the same order. Only one person lives between the floors of C and D who lives on any floor below the floor of
M. P lives on the floor immediately above the floor on which B lives. C lives on the third numbered floor. Only one person lives between the floors of M and N. M lives above N. Only two persons live between the floors of C and O.