1. The tickets (to bring) two days ago. 2. The key (to leave) at home. 3. The doctor (to send for) five minutes ago. 4. This book often (to ask for) in the li- brary. 5. The plans for the next holidays (to dis- cuss) yesterday. 6. This story (to write) at the last English lesson. 7. St. Petersburg (to found) in 1703 by Pe- ter I.

1. The tickets were brought two days ago.
Explanation: In this sentence, the verb "bring" is in the past tense. To change it to past simple tense, we add "-ed" to the base form of the verb, which is "bring." Therefore, the correct form is "brought."

2. The key was left at home.
Explanation: In this sentence, the verb "leave" is also in the past tense. We need to change it to past simple tense, so we add "-ed" to the base form of the verb, which is "leave." Therefore, the correct form is "left."

3. The doctor was sent for five minutes ago.
Explanation: In this sentence, the verb "send for" is in the past tense. We need to change it to past simple tense, so we add "-ed" to the base form of the verb, which is "send." Therefore, the correct form is "sent."

4. This book is often asked for in the library.
Explanation: In this sentence, the verb "ask for" is in the present tense. However, it is used to describe a habitual action (something that happens often), so we need to use the present simple tense. Therefore, the correct form is "is asked."

5. The plans for the next holidays were discussed yesterday.
Explanation: In this sentence, the verb "discuss" is in the past tense. We need to change it to past simple tense, so we add "-ed" to the base form of the verb, which is "discuss." Therefore, the correct form is "were discussed."

6. This story was written at the last English lesson.
Explanation: In this sentence, the verb "write" is in the past tense. We need to change it to past simple tense, so we add "-ed" to the base form of the verb, which is "write." Therefore, the correct form is "was written."

7. St. Petersburg was founded in 1703 by Peter I.
Explanation: In this sentence, the verb "found" is in the past tense. We need to change it to past simple tense, so we add "-ed" to the base form of the verb, which is "found." Therefore, the correct form is "was founded."

I hope this explanation helps you understand how to change the verbs to the correct tense. Let me know if you have any more questions!