As per the question, let a = 10, b = 5, c = 6, and d = 2. Plugging these into the answer choices, only C does not yield an integer.
a, b, c, and d are positive integers where a is divisible by b and c is divisible by d. Which of the following is NOT necessarily an integer?

(1) (ac) /(bd) 
(2) a/b + c/d
(3) (a + c) /(b + d) 
(4) (abc) /d
(5) (acd) /b