6) We know that only one of the following three relations is true: $x=5, x>5, x \leq 5$. Which of the following statements is definitely true?
(A) $x=5$
(B) $x \neq 5$
(C) $x>5$
(D) $x<5$
(E) $x \geq 5$.
6) The answer is (B).

It is impossible for the first relation to be true and the other two to be false; if only the second is true, it can be concluded that $x>5$, if only the third is true (and the first two are false), it can be concluded that $x<5$. Since both solutions are possible, it can only be concluded that $x \neq 5$.