sentences:  At the end of March 1989, Thatcher's six-day, 10,000-mile tour through southern Africa—a follow-up to her "look and learn" exercise in Kenya and Nigeria in 1988—did not include South Africa because Mandela had not yet been released.Thatcher met reformist F. W. de Klerk in London in June 1989 and stressed that Mandela must be freed and reforms put in place before she would visit the country.In July 1989 she called for the release not only of Mandela, but also Walter Sisulu and Oscar Mpetha, before all-group talks could continue.