Conversation so far:
What university did Achebe attend?
University College (now the University of Ibadan.
What year did he attend?
1948.
What did he study at the university?
He abandoned the study of medicine and changed to English, history, and theology.
Because he switched his field, however.

Question: What happened when he changed his field of study?
Self-contained rewrite: What happened when Chinua Achebe changed his field of study?