Which of the followings are tautology? A. (p∨r)→p B. p→(p∧r) C. ~p→(p→r) D. (p∧r)→(p→r) E. ~(p→r)→p

$(p\lor r)\to p$ fails when p is false and r is true, and $p\to(p\land r)$ fails when p is true and r is false, so A and B are not tautologies. $\lnot p\to(p\to r)$ is always true, because whenever $\lnot p$ holds, p is false and $p\to r$ is true; $(p\land r)\to(p\to r)$ is always true, because if $p\land r$ holds then r is true. $\lnot(p\to r)$ is equivalent to $p\land\lnot r$, which implies p, so E is a tautology too, giving C, D and E only.