In Sartre's philosophy, "bad faith" refers to the human tendency to deny one's own freedom by adopting a false sense of determinism or excuses. This denial undermines the assertion of one's own agency and freedom (A).
Furthermore, in Sartrean existentialism, nothingness is intimately connected with human freedom. The concept of nothingness is what allows for the possibility of freedom because it enables the transcendence of facts or given circumstances. By asserting the existence of nothingness, one affirms the ability to act freely (C).
Options (B) and (D) are incorrect. In Sartre's view, asserting nothingness does not deny freedom (contrary to option B), and being and nothingness are not contradictory in his framework; rather, nothingness enables being to transcend its factual limitations (D is incorrect).
\[
\boxed{\text{Therefore, (A) and (C) are correct.}}
\]