Example of unsatisfiable set of wffs, with each pair is satisfiable On page 66, A Mathematical Introduction to Logic, Herbert B. Enderton（2ed),

For each of the following conditions, give an example of an unsatisfiable set $\Gamma$of formulas that meets the condition.
(a) Each member of $\Gamma$ is—by itself—satisfiable.
(b) For any two members $γ_1$ and $\gamma_2$ of $\Gamma$, the set $\{γ_1, γ_2\}$ is satisfiable.
(c) For any three members $γ_1$, $γ_2$, and $γ_3$ of $\Gamma$, the set $\{γ_1, γ_2, γ_3\}$
is satisfiable.

Except for (a), I have difficulty in constructing examples of (b) and (c).

Why not something like: $a\implies b$, $\lnot a\implies c$, $b\implies \lnot a$ and $c\implies a$. You get a contradiction if all $4$ are true, but any three do not lead to contadictions.
