What Am I Riddles

Question: It takes one word to separate them; otherwise they are inseparable.

What are they?

Question: What kills a lot of people but is harmless?

Question: What grows shorter as it grows older?

Question: I was crucified to keep murders out of the maze. What am I?

Question: Sometimes, I leave you with “mixed” feelings. More times than not, I teach you a lesson. I give what I didn’t create. What am I?