Question: Leonora Mary Grosvenor's father was the richest man in Britain in what decade?
Sentence (from "Robert Grosvenor, 5th Duke of Westminster"): Lieutenant-Colonel Robert George Grosvenor, 5th Duke of Westminster, {'1': ", '2': ", '3': ", '4': "} (24 April 1910 – 19 February 1979) was a British soldier, landowner, businessman and politician.
Relevant evidence: No