Hello, fellas. How is it going? Today we are going to learn how to reduce relative clauses. According to Betty Schrampfer Azar, a relative clause is a dependent clause modifying a noun. Further information about a noun is described, identified, or given by the clause. It is also called an adjective clause.
(More on relative clauses: https://englishtips4u.com/2011/11/08/engclass-relative-clause/ and https://englishtips4u.com/2011/11/09/engclass-relative-clause-2/)
Relative clauses with relative pronouns as subjects (who, which, or that) can be reduced to adjective phrases.
There are two ways in which a relative clause is changed to an adjective phrase:
1) If the relative clause contains be, omit the pronoun and be.
Relative clause: The research which was conducted by the students is published.
Adjective phrase: The research conducted by the students is published.
2) If there is no be in the relative clause, omit the pronoun and change the verb to its –ing form.
Relative clause: Students who conduct research should write in journals.
Adjective phrase: Students conducting research should write in journals.
Betty Schrampfer Azar, Understanding and Using English Grammar: Third Edition