Which of the following best describes what led to london’s “killer fog” in 1952?

b. Millions of coal fires and stagnant air caused toxic fumes to build up in the air.

Actually, millions of coal fires and stagnant air caused toxic fumes to build up in the air. The air all around London was then incredibly toxic, and people struggled to breathe due to the fumes.

Is there possibly mutliple choice answers or is this a type/write it in question?

The answer is telescope.