Who:
1. The girl is sitting under the tree. She is my girlfriend.
→ The girl who is sitting under the tree is my girlfriend.
2. The man is talking to Julie. He is our CEO.
→ The man who is talking to Julie is our CEO.
3. The man lives next door. He loves Kate.
→ The man who lives next door loves Kate.
Whom:
1. That is my English teacher. I admire her.
→ That is my English teacher whom I admire.
2. I was invited to the party by James. I met him this morning.
→ I was invited to the party by James whom I met this morning.
3. He is my best friend's boyfriend. My cousin admires him a lot.
→ He is my best friend's boyfriend whom my cousin admires a lot.
