Correct option is B
Given - A, B, C, D, E and F live on six different floors of the same building. The lowermost floor in the building is numbered 1, the floor above it, number 2 and so on till the topmost floor is numbered 6.
The product of floors on which E and F live is 10.
A lives immediately above C.
The sum of floors on which B and E live is 11.

the sum of floors on which C and D live = 3 +1 = 4