1. Essential or Restrictive
1.1. That
1.1.1. The dog that my sister has is big and strong.
1.1.2. The wallet that my aunt bought is very expensive.
1.2. When
1.2.1. 2019 was the year when the COVID-19 began.
1.2.2. I still think of the day when we got lost in the mall.
1.3. Where
1.3.1. The store where we bought the bird food was closed in the morning.
1.3.2. The bookstore where we bought our books is not available today.
1.4. Who
1.4.1. The girl who danced tango in the parade is my friend.
1.4.2. The boy who took my book is my brother.
1.5. Whom
1.5.1. He does not know to whom he will give his work .
1.5.2. I spoke with whom I should have apologized for a long time.
1.6. Whose
1.6.1. He is the child whose father is the owner of this school.
1.6.2. Fernando is the boy whose sister has a chronic disease ; he is strong and a good person.
1.7. Which
1.7.1. I used the car which my brother bought me last week.
1.7.2. The cats which my mother brought me last weekend are lost.
1.8. Why
1.8.1. The noise of the cars is the reason why I prefer the countryside.
1.8.2. You're the reason why I won't go to the party.
2. Non-essential or Non-restrictive
2.1. That
2.1.1. That always indicates a clause that is essential to the meaning of the sentence because it defines or identifies the noun it refers to.
2.2. When
2.2.1. Summer was my favorite time, when we used to walk through the woods.
2.2.2. I don't like the Middle Ages, when the Spanish invaded us and stole our land.
2.3. Where
2.3.1. The school, where I used to eat while we were in class, no longer receives students in its classrooms.
2.3.2. The park, where my children practiced basketball, will be closed the following month.
2.4. Who
2.4.1. Sofia's mother, who is of Egyptian descent, cooked for my birthday.
2.4.2. Zaha Hadid, who built the London Aquatics Centre, is my favorite architect.
2.5. Whom
2.5.1. My sister met her favorite rockstar, whom she has loved since 12 years old.
2.5.2. I have never told you about my friend Carlos, with whom I enjoyed play videogames.
2.6. Whose
2.6.1. The teacher, whose wife owns a business,has changed his job.
2.6.2. Abbud, whose name sounds strange, has invited me to visit his country.
2.7. Which
2.7.1. The car, which belongs to the Lamborghini brand, is being repaired in North Texas.
2.7.2. The highway, which was built by the former government, is not in good condition and has many potholes.