Which of the following is a key importance of EU membership for Ireland?

The key importance of EU membership for Ireland lies in access to the Single European Market. This market provides Irish businesses with the opportunity to trade freely with other EU member states, eliminating tariffs and reducing trade barriers. This access enhances economic growth, encourages investment, and facilitates the export of goods and services, which is vital for Ireland's economy, given its reliance on exports.

In contrast, the other options do not capture the primary benefits of EU membership. Increased taxation does not inherently relate to the advantages of being part of the EU and can be influenced by various domestic policies. Limited trade agreements would imply a restriction on trade, which is contrary to the objectives of EU membership that generally aim to expand trade opportunities. Lastly, isolation from global markets contradicts the benefits of EU membership, which actively seeks to integrate member countries into wider international trade systems rather than isolating them.