Identify the use of the italicized noun clause.

the reason i am late is that i had failed to set the alarm.

direct object
subject
subject complement

The noun clause "that I had failed to set the alarm" is a subject complement.

Explanation:

A subject complement is a word, phrase, or clause that follows a linking verb and refers back to describe or complete the grammatical subject of the sentence.

In the given sentence, we have the linking verb is and the subject complement (the noun clause that I had failed to set the alarm) that describes or completes the subject of the sentence (The reason).

i may be wrong but i think your answer is flashback

i think the answer is c.