Answer :
"While I was walking home yesterday, I ran into my old first grade teacher." is a complex sentence.
One independent clause and at least one dependent clause make up a complex sentence. A clause is a set of words that consists of a subject and a predicate. The word that expresses the topic of a phrase or who or what is carrying out an activity is the subject.
One or more subordinate (dependent) clauses are added to the main (independent) clause by utilising conjunctions and/or relative pronouns to create a complex statement.
In this sentence, 'While I was walking home yesterday' is the subordinate clause and 'I ran into my old first grade teacher' is the independent clause. The hints we get is the word 'while' - Here, while is a subordinating conjunction.
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