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).

"The reason I am late" is the noun clause, and it is being used as a subject.

Explanation:

While no words are italicized here, I know this to be a noun clause because a clause contains a subject and a verb. So if all of these words are italicized, it is a subject. If "I am late" is italicized, it is a subject complement. Both of these contain subject and verbs, so without the italics, these should give you the answer.