5. Students will be punished. their homework is late

-> Students whose homework is late will be punished

6. I was looking for a book this morning. i've found it now

-> Now I've found the book (which) I was looking for this morning

7. Is that the car? you want to buy it

-> Is that the car (which) you want to buy ?

8. Sandra works in advertising. you were talking to her

-> Sandra, whom you were talking to, works in advertising

Chúc a/cj học tốt ạ!