Answer:
Granpa treats me as if I were still a baby.
Explanation:
I believe the italicized verb in the sentence is "was." In this case, you have to change "was" to "were."
A "subjunctive mood" indicates a situation that is not real. It could be hypothetical in nature, a wish, a demand or a suggestion. It can also be used in "that-clauses" and by using "as if/as though/if."
Remember that it doesn't use am/is/are/was, rather it uses "be" and "were."
For example: It looked as if she were already at the party.
If I were you, I'd look for a new partner.
