Answer: Nadia was delighted she got a part in the school play, though she knows it's a small one.
Explanation: A complex sentence is a sentence with 1 independent or 1 ore more dependent clauses, and a subject verb that can't stand alone, like you said.
Some complex sentences have keywords.
Keywords like: As, as if, before, after, because, though, even though, and so on. ("So on" isn't a keyword)
Complex sentences make sense; They have a complete sentence, and a subject + verb.
That being said, we can look back at the sentences and identify the subject, verb and keyword.
All of that being said, Number 3 is a complex sentence.
Number 3 is a simple sentence, meaning it has a independent clause.
Independent clause: Nadia was delighted she got a part in the school play.
This is what gets students confused. A independent clause MUST CONTAIN A SUBJECT AND A VERB.
Subject: School play.
Verb: School.
Hence, number 3 is a complex sentence.
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