C. that or whom
Feedback We became friendly with some students. We met them on the train. When we combine these two clauses into one, the relative pronoun should replace the object pronoun ‘them’. As you know, ‘who’ is in the nominative case. It is not possible here. Hence, we use ‘whom’. ‘That’ is also possible.We became friendly with some students whom we met on the train. OR We became friendly with some students that we met on the train.