Underline should or shouldn't. 17.I think I am getting a cold. I should/shouldn't take some vitamin C tablets. 18.She should/shouldn't go to the doctor. She doesn't look well. 19.Paula should/shouldn't worry. She always does well at Maths. 20.If you are tired, you should/shouldn't go to bed early tonight. 21. We should/shouldn't fight. We are best friends!

Решение:

1. I think I am getting a cold. I should take some vitamin C tablets. (Рекомендуется принять витамин С при простуде).
2. She should go to the doctor. She doesn't look well. (Если человеку плохо, ему следует обратиться к врачу).
3. Paula shouldn't worry. She always does well at Maths. (Нет причин для беспокойства, если человек успешен).
4. If you are tired, you should go to bed early tonight. (При усталости следует лечь спать пораньше).
5. We shouldn't fight. We are best friends! (Друзья не должны ссориться).

Ответ: 17. should, 18. should, 19. shouldn't, 20. should, 21. shouldn't.