1. She said that China is* a densely populated country.
2. Ann said that it was time they had moved to a new house.
3. He said that water freezes* below 0°C.
4. She said that she had been reading the children a story the previous night when the lights had gone out.
5. He told me that he would help me to repair my car the next day.
6. He said that he hadn't understand the meaning of the film.
7. She told him that he could come to her if he had any problems.
8. He told her that he had seen the film she had recommended the previous night.
9. He said that he was going to Spain the following week.
10. He said that she didn't understand.
11. He said that he would have invited many people if he had had a bigger flat.
12. He told us that he wouldn't repeat that again.
13. He said that he had applied for several jobs that week.
14. He told me that he was afraid he couldn't come.
15. He told her that if he finished it that evening, they would go out.
16. She said that she had seen him the day before but he hadn't recognised her.
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is/freezes* - в данных случаях мы имеем полное право ничего не изменять в предложениях. Связано это с тем, что информация, которую несут данные предложения, всегда является действительной, вне зависимости от говорящего. Например, если я сказал когда-то в прошлом, что Мадрид - столица Испании, то от моих слов ничего не изменится: Мадрид как был столицей Испании, так он ей и остался. Поэтому, "I said that Madrid is the capital of Spain".