Read this: The BBC is also renowned for its production of costume dramas, such as Jane Austen's Pride and Prejudice and contemporary social dramas such as Boys from the Blackstuff and Our Friends in the North. The BBC has come under pressure to commission more programmes from independent British production companies, and indeed is legally required to source 25% of its output from such companies by the terms of the Broadcasting Act 1990. Programmes have also been imported mainly from English-speaking countries: notable—though no longer shown—examples include The Simpsons from the United States and Neighbours from Australia. Because of the availability of programmes in English, few programmes need use sub-titles or dubbing unlike much European television.

What year was the Independent Broadcasting Act written?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable