The relative clause is non-defining, and therefore 'that' is incorrect; only 'which' is used in such clauses. 'That' with no preceding comma would make in a defining relative clause. That would not be appropriate in this sentence.
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AnonymousThe relative clause is non-defining, and therefore 'that' is incorrectI thought "studied linguistics" is defined by a relative clause either "which" or "that" in the sentence. But what you mean is the relative clause "which?" (that?) is non-definining for "studied linguistics"? (I know a relative clause "that" preceded by a comma can't be used thus n