11. Mary went to bed early because she felt tired.

⇒ Because of having felt tired, Mary went to bed early.

12. She stayed at home because her mother was sick.
⇒ Because of her mother's sickness, she stayed at home.

13. John succeeded in his exam because he worked hard.

⇒ Because of having worked hard, John succeeded in his exam.

14. Despite the narrow streets, many people drive cars in this city.

⇒ Though the streets is narrow, many people drive cars in this city.

15. I like him because his father is kind to me.

⇒ Because of his father's kindness to me, I like him.

16. I couldn’t do the test because it was difficult.

⇒ Because of the difficulty of the test, I couldn’t do.

18. In spite of his age, he still leads an active life.

⇒ Even though he is old, he still leads an active life.

19 Peter couldn’t return home because of losing all her money.
⇒ Because Peter lost all her money, she couldn’t return home.

20. In spite of the high prices, my daughters insist on going to the movie.

⇒ Although the prices are high, my daughters insist on going to the movie.