Who or whom 2

Do you have problems choosing between the pronouns who and whom? Many people do. Here's a tip: use who as the subject of a verb and whom as the object of a verb or preposition.

1. Placeholder for the answer can possibly be calling me at this time of night?
2. Placeholder for the answer did Sergei visit yesterday?
3. To Placeholder for the answer can we turn to find the answers to these questions?
4. Placeholder for the answer shall I say is calling?
5. Cara wondered Placeholder for the answer voters would choose as the next leader of the country.
6. Isabella is the girl Placeholder for the answer solved the problem.
7. Placeholder for the answer shall I say sent me?