Homework on §1.4--assigned Fri 9/1 and due Mon 9/4

Suppose you know that φ, ψ, χ ⇒ θ but φ, ψ ⇏ θ (i.e., the entailment no longer holds if you drop the premise χ). What does that tell you about the patterns of truth values that are possible for the premises φ, ψ, and χ? Briefly explain you answer using the definition of entailment.