Cleo added 3a+4b and got 7ab. Three of these statements explain why her answer is wrong. Which one does not

Answer:
3 and 4 are factors of 12 so they should be multiplied to get a product of 12 ab. (Answer D)
Step-by-step explanation:
You do not multiply in addition unless an exponent is present. You should not multiply or add considering these are not like terms. Therefore, D is wrong.