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Solution

Given grammar is:

$S\to SbS\mid a$

This grammar is ambiguous.

The string is:

$abababa$

It contains $4$ symbols $a$ and $3$ symbols $b$.

This is like combining four $a$'s using three $b$ operators.

Because the grammar does not define a fixed grouping rule, the string can be derived in more than one way.

For example, one possible grouping is:

$(((a)b(a))b(a))b(a)$

Another possible grouping is:

$(a)b((a)b((a)b(a)))$

So, the string has more than one parse tree.

For every different parse tree, there is a corresponding different left most derivation.

So, it has more than one left most derivation.

Similarly, for every different parse tree, there is a corresponding different right most derivation.

So, it has more than one right most derivation.

Therefore, all three statements are true in the sense of ambiguity.