The correct answer is Lacklustre performance of the service sector. Explanation & Key Takeaways: • The South-East Asian crisis during 1997-98 was a significant economic event that impacted many countries in the region. • However, it was not a direct contributory factor for widening the trade deficit in Australia since 1991. • The other three options (increasing competition from China, lacklustre performance of the service sector, and non-tariff barriers created by trading partners) have been more consistently associated with the widening trade deficit. • South-East Asian crisis during 1997-98: This crisis caused a significant economic downturn in many Southeast Asian countries, which reduced their demand for Australian exports. However, the overall impact on Australia's trade deficit was relatively modest, and it cannot be considered a major long-term factor. • Increasing competition from China: China's emergence as a major manufacturing power has led to increased competition for Australian exports in many markets, particularly in labor-intensive industries. This has contributed to the widening trade deficit, as Australian producers face challenges in maintaining their competitiveness. • Lacklustre performance of the service sector: The service sector accounts for a significant portion of Australia's economy, but its performance has been relatively lackluster in recent years. This has limited the growth of services exports, which could have helped to offset the widening trade deficit.