Hello, Coco, and happy New Year.
"such" can be used at the beginning and cause inversion only when it is an independent intensifier, that is, when it can be used alone.
Notice that with "a strong public opinion" the intensifier "such" will form part of the phrase: such a strong public opinion. We cannot say: The strong public opinion was such... Instead, we could say: The public opinion was so strong..., which can be inverted as:
- So strong was the public opinion that...
However, we can say:
- The strength of the public opinion was such... (notice that such appears alone in the predicate)
and this can be inverted as:
- Such was the strength of the public opinion that...
Therefore, the correct option is (3).