Ответ:
- Monday is the 1st day of the week.
- Tim was the 4th child in the family.
- December is the 12th month of the year.
- She was born on the 23rd of November.
Все предложения составлены верно!
Лайфхак: Всегда обращай внимание на артикли the/a, чтобы не допустить ошибку!