The role of Garibaldi in the Italian Unification, The Archers since 1970, the science-fiction novels of Arthur C Clarke, and rivers of Britain and Ireland are specialist subjects in the first of the semi-finals.
8.30 The life and work of physicist Niels Bohr, the "Culture" novels of lain M Banks, the life and career of Warwick the Kingmaker and the life and films of Barbara Stanwyck are the specialist subjects in the second semi-final. The final is next week.
Director Derek Hallworth ; Series producer Pam Cavannagh
www.bbc.co.uk/mastermind