Answer:
C. noun clause
Explanation:
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.
The clause whether everyone will be on time acts as a direct object:
I do not know something (your schedule/ this grammar rule/ his birthdate, etc.). That means "whether everyone will be on time" is a noun clause.
