Inspect your home
Be very careful with space heaters.
Check your appliances.
Check the air conditioning and heating unit in your home.
Check the natural gas/LP gas system in your home.
you did not say any option
I believe the answer is ᴠɪʀᴜs.
hopefully that helps:)
Because, when an infection exist in the human body it tends to spread, so if the cells stayed in one space then the infection would have a much greater opportunity to severly make that person very ill before the cells could even get to the infection.
D) Coping with difficult situations