Which C.S. Lewis book adapts his 1941 BBC radio talks about Christianity?

Mere Christianity adapts C.S. Lewis’s 1941 BBC radio talks about Christianity.

Lewis first delivered the talks during the Second World War, when the BBC broadcast them to a wide audience in Britain. He later revised and combined the material into three sections: Broadcast Talks, Christian Behaviour, and Beyond Personality. The complete book was published in 1952.

The title refers to Lewis’s attempt to discuss shared Christian beliefs rather than defend one denomination’s distinctive doctrines. The book is not a biography and is not the same work as The Problem of Pain, which examines suffering and was published in 1940. Mere Christianity became one of Lewis’s most influential works of Christian apologetics and helped establish his public reputation as a religious writer as well as a novelist and literary scholar.