Prove/Disprove: Let $M$ such that for every $a\in D$ (the domain) there's a term $t$ such that $t\mapsto a$,in $M$.
Claim: a clause $\exists xA$ is true in $M$ iff there is a term without free variables such that $A\{\frac{t}{x}\}$ (meaning, substitution of $x$ with $t$) is true in $M$.
My guess is that this claim isn't true, but a I cannot find a good example to demonstrate it.
I'd be glad for help!