Answer:
The modifier in the sentence, “Tom ate the burger and fries as if he were in a race,” is “as if he were in a race.”
Step-by-step explanation:
A modifier is a section of a phrase or a clause structure. In English grammar, the responsibility of a modifier is to modify or change another element in the structure of a sentence on which this optional element is dependent.
In this sentence above, “as if he were in a race” is the modifier which changes the other element of the sentence structure. Plus, the first part of the sentence if separated from the modifier forms an independent statement. So, “Tom ate the burger and fries,” is an independent sentence which is grammatically correct and is equal in structure to the original sentence.