English grammar rules: independent clauses When do we use that instead of which? When do we need a comma after the clause? Ex: A learned that the real challenge encountering in international business acquisition is the lack of management competency on resource integration. "encountering... acquisition" modifies challenge. A conduct a systematic study on international business acquisition, earning himself an honer. "earning... honer" modifies the main clause. Can I write like this : A conduct a systematic study on international business acquisition that/which earning himself an honer. "that/which earnin... honer" modifies a systematic study OR A conduct a systematic study on international business acquisition, that earning himself an honer. "that/which earnin... honer" modifies the main clause.