What did Tom eat in addition to the hamburger?

In this context, the correct answer indicates that Tom consumed something else along with the hamburger, which is not specified in detail. The word "also" suggests that Tom ate more than just the hamburger, implying an addition to his meal. It serves as a connector that indicates the presence of further items in his meal, thus effectively conveying the idea of additional food without providing specifics about what that might be.

In comparison, the other options either provide specific food items or lack clear relevance. "Fries" and "soup" suggest particular additions to the hamburger, while "nothing" contradicts the premise that he ate something additional. Thus, "also" correctly captures the intent to communicate that there was more food but leaves the details open-ended.