Is the underlined phrase an adjective phrase or an adverb phrase?

early in the morning, the animals begin the search for

food.

a.
adverb phrase

b.
adjective phrase

Early in the morning, the animals begin the search for food.

A.  adverb phrase

Explanation:

An adverb phrase is a kind of prepositional phrase that functions as an adverb. Therefore, it answers the questions Where? When? How? or Why?  and can modify a verb, an adverb, or an adjective.

In this sentence, the underlined phrase is in the morning. It is an adverb phrase because it modifies the adverb 'early'.  It is answering the question "When?"  

i think that will have something to do with the mississippi river but google will know the full answer for sure

d is the best answer for this question.