Which C.S. Lewis book collects his 1940s BBC broadcasts about Christianity?

Mere Christianity collects and revises C.S. Lewis's BBC radio broadcasts about Christian belief. The talks were delivered during the early 1940s, beginning with The Case for Christianity in 1941.

Lewis aimed to explain shared Christian ideas in accessible language rather than defend one denomination. The resulting book is arranged in four parts: “Right and Wrong as a Clue to the Meaning of the Universe,” “What Christians Believe,” “Christian Behaviour” and “Beyond Personality.”

The Problem of Pain and Miracles are separate Lewis works. Christian Behaviour was one broadcast series and later formed part of Mere Christianity, not the title of the complete collection.