As per the question, let x = 2, y = 6, and z = 12. Plugging these into the answer choices, only A does not yield an integer.
If x, y, and z are positive integers such that x is a factor of y and y is a factor of z, which of the following is NOT necessarily an integer?
Options:
  - (x + y) /z
  - (y + z) /x
  - yz/x
  - (2y + 3z) /x
  - (xy + z) /y