Answer:
In New York City in 1900.
Step-by-step explanation:
I can vividly remember learning about prepositional phrases when I was in 7th grade because we always did exercises on them as a full class! So fun. :)
Prepositional phrases are those that begin with a preposition, and essentially finish the rest of the sentence. So, in this case, "The first automobile show was held" would be the first part of the sentence, while "In New York City in 1900" would be the second part/prepositional phrase of the sentence.