I Have Observed That Some of the Bad Smell in My

I have observed that some of the bad smell in my house is caused by my cat.Which of the following observations would allow me to use the method of residues to show that there is a second cause of the bad smell?

A) finding a piece of rotting cheese under the refrigerator
B) pouring different amounts of sour milk onto surfaces in different rooms to see whether the smell changes or not
C) confining the cat to a bedroom and then observing how quickly the smell of the bedroom changes
D) cleaning the house thoroughly and then observing whether or not the smell changes
E) removing the cat from the house and then observing whether the bad smell remains