Supply a suitable adverb clause to complete the sentence:
                            , our class plans to go for an outing.
a) After the final exams
b) Now that the final exams have ended
c) During the summer holidays
d) None of the above

Hint: Adverb clauses often begin with a subordinate conjunction.

Complete step by step answer:
An adverb clause is a group of words that contains a subject and a verb, and this group functions as an adverb, by thus modifying an adjective, verb or an adverb. Adverb clauses generally begin with subordinate conjunctions like because, while, etc.

Let us analyze the options given to us in this question:
Option (a.), 'After the final exams', is incorrect because it is a phrase, not an adverb clause.

Option (b.), ‘Now that the final exams have ended', is correct since it is an adverb clause of reason. 'Now that' is a pair of conjunctions that refers to the cause or reason "final exams have ended". The subject here is ‘final exams’, and the verb is ‘ended.’

Option (c.), ‘During the summer holidays',is incorrect because it is a phrase, not an adverb clause.

Option (d.), ‘none of these', is incorrect as the given option (b.) is correct.

Note: Any option without both a subject and a verb is not an adverb clause.