Which statements correctly classify relative-clause structures? Select all that apply.
A comma-marked clause about an already identified person may begin with who.✓Correct answer
A defining object relative may omit its relative pronoun.✓Correct answer
A non-defining clause may begin with that after a comma.
A subject relative pronoun may always be omitted in a defining clause.
Explanation
Who is standard in a non-defining clause about a known person, and an object marker may disappear from a defining clause. That is barred after the comma of a non-defining relative, while omission cannot remove a subject relative marker.