Is it right to tell
- Five years ago he already knew that two plus two equals four.
or
- 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?