Among the continents listed, Australia is typically considered difficult to connect to via traditional trade routes compared to others like Europe, Asia, North America, and Africa. If Australia is not an option and you are only considering the ones listed, Africa might also be a continent that has more challenges in terms of infrastructure and connectivity compared to Europe, Asia, and North America. However, specific difficulties would depend on the context of trade routes and current geopolitics.
If you meant to list Australia, please confirm. Otherwise, from the options provided, Africa could be a valid response.