Упр.3 Уроки 3-4 Юнит 6 New Millennium English 11 класс

In the text find the words which mean:

1. one part of a large subject of study or knowledge
2. something that must happen first before something else can happen
3. extremely important or necessary in order to do something successfully
4. leaving out or not including
5. to try and find out the truth about something
6. to watch something or someone carefully
7. correct or normal way of doing something
8. asking someone to imagine that a particular situation existed