Ответ:

2. Was there/ Yes, there was. There was a garden.

3. Were there/ No, there weren’t. There were three flags.

4. Were there/ No, there weren’t. There was one fountain.

5. Were/ Yes. There were two horses.

Объяснение:  

Was единственное число

Were множественное

2. Was there

Yes, there was a garden outside the castle

3. Were there

No, there were three flags on top of the castle

4. Were there

No, there was one fountain outside

5. Was there

Yes, there was one horse

Was это как am/is, но в прошлом

Were это как are в прошлом