The correct answer is A.
Hunger, chemical imbalance, and blood levels are all internal issues. Cat dander on the other hand is not something the body creates or and is something in the environment.
Thus, your answer is A.
You should clean up after every investigation because if you leave a mess, maybe another detective will come in and get lost because of the mess you left.
A p sub- level has 3 sub levels so it contains 6 electrons max