A dependent clause that modifies a noun. (Functions as an adjective - answering What kind?; How many?; Which one?) Typical Constructions: 1. Relative pronoun + subject+ verb 2. Relative pronoun as subject + verb Relative pronouns: Who, whom, whose, that, which EX: He recognized the woman WHO WAS WALKING PAST. She swept up the cereal THAT HAD FALLEN FROM THE TABLE. We drove past the house IN WHICH MY MOTHER HAD LIVED. In English, sometimes the relative pronoun is absent (yet implied). EX: The sandwich I had for lunch was delicious! The sandwich (that) I had for lunch was delicious!

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Here you will find all the information about "adjective clauses": http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/adj.htm