Which best identifies the underlined clause?
he understood (that the tomb might be there and still be untouched.)
a. adjective clause b. independent clause c. adverb clause d. noun clause

The answer is D, noun clause. A noun clause is a dependent clause that acts as a noun. Noun clauses begin with words such as how, that, what, whatever, when, where, whether, which, whichever, who, whoever, whom, whomever, and why. Noun clauses can act as subjects, direct objects, indirect objects, predicate nominatives, or objects of a preposition. It cannot be an adjective clause because it changes the meaning of the sentence. It cannot be an independent clause because it cannot stand on its own. And it cannot be an adverb clause because it does not describe a verb nor answer the questions how when or where.