Correct the sentences, if there is not mistake, write RIGHTПримечания к

Correct the sentences, if there is not mistake, write RIGHT
Примечания к заданию: Исправить предложения, если в их нет ошибок, написать слово "Right". 1 и 2 как эталоны.
Если встретили Past Perfect, то меняем на Past Simple (Повстречается 2 раза!)
Во всех остальных предложениях необходимо будет поменять Past Simple на Past Perfect, может быть только 1 глагол в Past Simple, который необходимо будет поменять, необходимо будет отыскать его, как я сообразил это когда деяние совершено в прошлом, но имеет связь с настоящим. На вас вся надежда.

1. I was pleased to see my old college friends at the conference last week as we didnt see each other since we finished our course as we hadn's seen
2. We had to wait for hours at the airport because the bad weather had delayed all the flight Right
3. Many Modern medicines were not invented by western scientists but by tribal people who had been used them for generations before the Europeans arrived.
4. We missed our train, so by the time we reached the theatre , the play ended and audience was leaving the theatre.
5. At the end of their meal they found they couldnt pay the bill because they didnt bring any money with them.
6. The children were thrilled when they unwrapped the electronic toys, but when they discovered that nobody bought a battery they were very disappointed.
7. When I came out of the cinema I had found that a thief took my car radio.
8. At first the authorities thought the athlete had been taking drugs, but they soon realized they mixed up the results of the tests.
9. When the film star came into the restaurant I didnt recognize her because I didnt see any of her films
10. When we reached the city centre we couldnt find a parking space, so we had decided to go by bus the nest time.