For a grammar to LL(1), there should be no conflict in
- FIRST(A) and FIRST(S)
- FOLLOW (A) and FIRST(A)
- FOLLOW(S) and FIRST(S)
Considering the above grammar, let us hit the condition that there is no common value in FIRST(A) and FIRST(S)
Option-1: A -> ep
Then FIRST(S) = {a,b}
FIRST(A) = {ep}
==> No Conflict
Option-2: A -> a/ep
Then FIRST(S) = {a,b}
FIRST(A) = {a}
==> Conflict
Option-3: A -> b/ep
Then FIRST(S) = {a,b}
FIRST(A) = {b}
==> Conflict
Option-4: A -> a/b
Then FIRST(S) = {a,b}
FIRST(A) = {a,b}
==> Conflict
So Option-1 is the Answer
