Which of the following is a common denominator of 1/4 and 5/6

12 is both a common denominator of 4 and 6, as they are both factors of 12.
Hope this helps :)

12 is a common denominator of 1/4 and 5/6 because 4x3=12 and 6x2=12. :) Good luck and happy holidays! 

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.