Bring me the largest head of lettuce, please.

I have to pick out the prepositional phrase and then identify its object.

of lettuce (pp phrase) lettuce (it object)

Right.

To identify the prepositional phrase and its object, you can follow these steps:

1. Read the sentence: "Bring me the largest head of lettuce, please."
2. Look for prepositions: In this case, the preposition is "of."
3. Identify the object of the preposition: The object of the preposition "of" is "lettuce."

So, in this sentence, "of lettuce" is the prepositional phrase, and the object of this phrase is "lettuce."