Question: How many Grand Slam singles titles did the tennis player, who defeated Hana Mandlíková, during the 1988 Australian Open – Women's Singles, win?
Sentence (from "Steffi Graf"): Stefanie Maria "Steffi" Graf (] ; born 14 June 1969) is a German former tennis player, who was ranked world No. 1 during her career.
Relevant evidence: No