Is it right to tell
- Five years ago he already knew that two plus two equals four.
- Five years ago he already knew that two plus two equaled four.
On English classes (I live in not English speaking country) we have learnt that if present clause is dependent to past one than it turns into past. However, I did not fully agree with it and gave (the top sentence above as) an example. It caused a lot of confusion.
In my country's official pre-university English exams (one of the previous years' variants) there is a text with tasks. One of the sentences is:
Nurse believed that fresh air and food ____ very important in fighting soldiers' diseases. A. are B. were ...
I was really surprised when I discovered that the right answer is B. were.
My logic is: when nurse dies, it won't become unimportant. That's why A. are should be right.
Could someone please help figuring it out?