Select the letter of the term that identifies the phrase in parentheses in the following sentence: artificial blood serum may soon be made (with potato protein).

a. prepositional phrase
b. appositive phrase
c. participial phrase
d. gerund phrase
e. infinitive phrase

The phrase with potato protein is a A. prepositional phrase, since it begins with the word with, which is a preposition. 
An appositive phrase would be separated with commas, a participial and gerund phrase would have the form verb + ing (making...), and infinitive phrase would have an infinitive (to make).