An adverb clause is a subordinate clause that modifies a verb, adjective, or another adverb.
It begins with a subordinating conjunction.
It tells how, when, where, why, or what to extend.
5. The birds flew away from the road once they saw the car coming.
This is an example of how the adverb clause is in the middle of the sentence. The adverb describes how the birds flew away when they saw the car coming.