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Each of nine persons. P, Q, R, S, T, U, V, W and X, lives in a different flat in an apartment building, which has six floors (excluding the ground floor, which is used only for parking) and three flats on each floor. The three flats on each floor are in a row and no two adjacent flats on a floor are occupied. At least one person lives on each floor.

Further the following information is known:

1. P and Q live on the same floor.
2. R and S live on different floors.
3. T lives in the middle flat on the fourth Floor.
4. U lives on the sixth floor and V lives on the first floor.
5. W Fives on the floor which is immediately above the floor on which X lives.

If Q lives on the third floor, then how many combinations of persons could live on the second floor?

1. $8$
2. $6$
3. $5$
4. $7$

1