A grammar G is LL(1) if and only if which of the following conditions hold for every pair of distinct…

A context-free grammar is LL(1) if and only if for every pair of distinct productions $A \to \alpha \mid \beta$, all three conditions hold: (I) $\alpha$ and $\beta$ do not derive strings beginning with the same terminal symbol $a$, (II) at most one of $\alpha$ and $\beta$ can derive the empty string $\lambda$, and (III) if one alternative derives $\lambda$, the First set of the other alternative is disjoint from $\text{Follow}(A)$. Therefore, all of I, II and III are required.