Select the option that will improve the underlined part of the given sentence. In case no improvement is needed select ‘No improvement required’.
Fierce competition against restaurants has driven up the prices.

The given sentence talks about an undefined number or a group of restaurants.
The preposition 'among' is used when talking about people or things that are not distinct and are viewed as a group.
Example: A decision that has caused a lot of anger among women.
Therefore the word 'against' must be replaced with the preposition 'among' to make the sentence grammatically correct.
Hence option 2 is the correct answer.