Explain the concept of noun clauses.

Noun clauses are dependent clauses that function as nouns within a sentence. They can act as subjects, objects, or complements in a sentence.

A noun clause typically begins with a subordinating conjunction such as "that," "whether," "if," "why," or "wh-" words like "who," "what," "where," "when," "how," etc. These clauses can be introduced by question words or by words that indicate uncertainty or doubt.

For example:
- Subject: "What she said" surprised me. (The noun clause "What she said" acts as the subject of the sentence.)
- Object: I don't know "where he went." (The noun clause "where he went" acts as the direct object of the verb "know.")
- Complement: Her biggest fear is "that she will fail." (The noun clause "that she will fail" acts as the complement of the verb "is.")

Noun clauses can also be used as the object of certain verbs or prepositions, such as "believe," "think," "hope," "want," "after," "before," "in," "on," etc.

It is important to note that noun clauses can be transformed into direct or indirect questions. For example, the noun clause "I wonder if he will come" can be transformed into the direct question "Will he come?" or the indirect question "I wonder whether he will come."

Overall, noun clauses play a crucial role in sentence structure by functioning as nouns and adding depth and complexity to the sentence.