Complex sentence: Corus Group was formed through the merger of Koninklijke Hoogovens and British Steel on 6 October 1999 and was a constituent of the FTSE 100 Index until it was acquired by Tata in 2007.
Split into simpler sentences: Corus Group was formed through the merger of Koninklijke Hoogovens and British Steel on 6 October 1999. It was once a constituent of the FTSE 100 Index but was acquired by Tata in 2007.