주어 찾기 좀 도와주세요

영어 문장에서 주어를 찾고 있는데요.
아래 문장들의 주어가 무엇인지 알려주실 수 있을까요?
1. In the fifteenth century an Italian scientist invented a way of writing a message on the white of boiled egg.
2. Overnight fans slept outside the stadium to make certain they could get tickets.
3. Everything was silent and then there came a strange knocking at the door.
4. There are many important issues facing the world today, including unemployment, health care and overpopulation.