Good Riddles

Question: People pick me, and watch me until they give me power. Then they don't stare in my eyes. What am I?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: Living I do not exist. Dead I am an inspiration. You always doubt me. But never reject me. I am what is given from old to young. Without me people would not learn mistakes. What am I?

Question: Waking up I see a smile as warm as fire. Sleeping I see a gaze as cold as ice.

Question: Which triangle will have a larger perimeter : 3,4,5 or 3,4,7 ?