The translation of that conjecture is "if a number is divisible by 5, then it is also divisible by 10". Saying "divisible by 5" is another way of saying "multiple of 5". This conjecture is false because the value 25 is a multiple of 25 (5*5 = 25) but it is not a multiple of 10. We only need one counter-example to prove the entire statement to be false. Why? Because the statement implies that it works for every multiple of 5, but we've shown it fails with 25.
Answer: Choice C) 25
