Решите уравнение : 15 : а + 13 = 30

Поставьте предложения в вопросительной и отрицательной формах.

1. We were able to read that article in the library. 2. Some students will be permitted to take exams in December. 3. You have to read this book. 4. We shall be able to skate in winter. 5. My friend is to take part in the conference. 6. The students of our group had to go to the plant last week. 7. They were allowed to continue their research.