Answer:
The correct option is a.on the cake
Explanation:
A phrase is commonly defined as a unit or group of words that form part of a clause or a sentence. Unlike clauses, phrases do not contain a subject and verb therefore, they cannot convey a complete thought or idea.
Bearing in mind the stated above, it could be said that in the sentence "Christine blew out the candles on the cake and opened her presents", the phrase is the option a.on the cake since this option not only does not contain a subject and verb but also does not convey a complete thought or idea.
