The correct option is A A country could keep some of the advantages of being in the European Union with an association agreement, such as the one Norway has, but it would find it much harder to influence trade and competition policy.
A country could keep some of the advantages of being in the European Union with an association agreement, such as the one Norway has, but it would find it much harder to influence trade and competition policy. - Correct - A country could keep ........... but it would..........
A country that keeps some of the advantages of being in the European Union with an association agreement, such as the one Norway has, but would find it much harder to influence trade and competition policy. - Incorrect - Changes the meaning
A country could keep some of the advantages of being in the European Union with an association agreement, like the one Norway has, but it would find it much harder to influence trade and competition policy. - Incorrect - usage of 'like' is incorrect
A country could keep some of the advantages of the European Union with an association agreement, as Norway has, but it would find it much harder to influence trade and competition policy. - Incorrect - usage of 'as' is incorrect
A country could keep some of the advantages of being in the European Union with an association agreement, such as the one Norway has, and yet find it much harder to influence trade and competition policy. - Incorrect - Usage of 'and' distorts the contrast