1. Prove the proposition by contradiction: If $p$ then $q$, the first step is to assume the proposition is not true. The correct assumption is ( ).
(A) If $p$ then not $q$
(B) If not $p$ then $q$
(C) If not $p$ then not $q$
(D) $p$ and not $q$
-、1.D.
The negation of “if $p$ then $q$” is no longer any of the “four types of propositions,” but rather represents a “conjunction” proposition: $p$ and not $q$.