The jumbo sausage was delicious.That jumbo jet looks huge.
Elephant is a jumbo size animal
At my house I have a jumbo pencil
The sentence "the hardest part was choosing a good topic" is a noun phrase. In this context, it functions as the subject of the sentence, with "the hardest part" being the main noun phrase that is described by the complement "was choosing a good topic." The phrase encapsulates a specific idea or concept, emphasizing the difficulty of the decision-making process.
It functions as a subject of the sentence.
a sentence phrase is a"sentence "that funtions as a phrase in the sentence. For example: I'm tired of his saying " I'm out of money".
It is a sentence fragment and a noun phrase.
You would not use 'reason out' as a phrase in a sentence, the juxtaposition of those to words together is not good English.
Echoing a key phrase or word
A phrase is an unfinished sentence or a quote.
subject
subject