`a)`
`C1`: `M = {x | x ∈ N | x ≤ 7}`
`C2: M = {0;1;2;3;4;5;6;7}`
`b)`
`C1: P = {n | n ∈ N* | 21 < n ≤ 26}`
`C2: P = {22;23;24;25;26}`
`c)`
`C1: M = {n | n ∈ N | n ≤ 5}`
`C2: M = {0;1;2;3;4;5}`
`d)`
`C1: P = {x | x ∈ N* | 13 < x ≤ 17}`
`C2: P = {14;15;16;17}`