A cat thinks that you are opening a can of cat food when it hears the can opener.
A dog shying away from a magazine or newspaper, if the owner has used one to swat the dog as punishment.
If humans are ok to use as examples, A child learning that a stove is hot by touching it.
Saliva,unprotected intercourse,contact with infected blood (blood transfusion)
and women with an unborn child.
Answer: by the addition of one phosphate group
Explanation:
