Ответ

Чтобы вставить правильные формы глаголов to be в предложения, давайте разберем каждый случай:

1. Yesterday, I was at the library.
2. My sister wasn't happy about her birthday party.
3. They were in the same class last year.
4. The cats were in the garden last night.
5. We are excited about the vacation.
6. She was my best friend when we were kids.
7. The children are playing in the park.
8. It was a sunny day last Saturday.
9. Our teacher was very kind to us.
10. We were at the concert last week.
11. My parents were on a trip last month.
12. The books are on the table, but now they are gone.
13. Tom and Alice were at the zoo yesterday.
14. I am sure about the answer to that question. (not)
15. The movie was so interesting!
16. They were grateful for your help.
17. The cookies were delicious!
18. The flowers are blooming in spring.
19. You are right.
20. The film wasn't good. It was boring.

Объяснение:

• Was/Were: Используются для прошедшего времени. Was употребляется с единственными числами (я, он, она, оно), а were с множественными (мы, вы, они).
• Wasn't/Weren't: Отрицательные формы, соответственно.
• Am/Are: Используются для настоящего времени. Am используется только с "я", are с "ты", "мы", "вы", "они".