How is the CAP'S noun clause used in this sentence?

What I want to know is HOW ARE WE GOING TO PAY FOR THIS.

A. Subject
B. Direct Object
C. Object of a Preposition
D. Predicate Nominative

See your post below.

In the given sentence, the CAP'S noun clause "HOW ARE WE GOING TO PAY FOR THIS" is used as the subject.

Therefore, the correct option is:
A. Subject

In order to determine how the CAP's (complementizer, adjective, or adverb phrase) noun clause is used in the sentence "What I want to know is HOW ARE WE GOING TO PAY FOR THIS," we need to identify the function of the noun clause itself.

The noun clause, which starts with the word "how," functions as the object of the verb "is" in this sentence. The verb "is" links the subject "What I want to know" to its complement, which is the noun clause "HOW ARE WE GOING TO PAY FOR THIS."

Therefore, the correct answer is:

C. Object of a Preposition