Question

Choose a suitable adverb clause to complete the sentence:
, I saw that the corridor was empty.

• A. When I entered school
• B. On entering school
• C. And I entered school
• D. None of the above

Answer 1

The correct option is A When I entered school

An adverb clause is a group of words containing a subject and a verb, and it functions as an adverb, by modifying an adjective, verb or an adverb. Adverb clauses generally begin with a subordinate conjunction (since, because, while, etc.).
Option A is correct because it is an adverb clause of time, 'when' is a subordinate conjunction that refers to time.
Option B is incorrect because it is a phrase, not a clause.
Option C is incorrect because it is a coordinate/independent clause whereas an adverb clause is subordinate/dependent.
Option D is incorrect because the answer lies in A.