A research center created a public archive which local teachers could search without special software. The archive, which was updated every Friday, included short summaries of environmental studies. Some reports described sensors on which coastal teams depended during storm warnings. New readers often circled the noun before which and stopped there. Their tutor asked them to rebuild the missing part of each relative clause. In “which local teachers could search,” the verb search lacked an object. In “which was updated,” the relative word filled the subject position. In “on which coastal teams depended,” which was the object of the preposition on. After identifying those roles, the readers temporarily set the relative clauses aside and recovered the main statement: the center created an archive, and the archive included summaries. Finding the antecedent answered what the clause modified; finding the gap answered what role the relative word played inside the clause.