Passage: Parfit was born in 1942 in Chengdu, China, the son of Jessie (née Browne) and Norman Parfit, medical doctors who had moved to Western China to teach preventive medicine in missionary hospitals. The family returned to the United Kingdom about a year after Parfit was born, settling in Oxford. Parfit was educated at Eton College. From an early age, he endeavoured to become a poet, but he gave up poetry towards the end of his adolescence. He later studied Modern History at the University of Oxford, graduating in 1964. In 1965–66 he was a Harkness Fellow at Columbia University and Harvard University. He abandoned historical studies for philosophy during the fellowship, returning to Oxford to become a fellow of All Souls College.

Question: What did Parfit's parents teach in China?
preventive medicine