What Am I Riddles

Question: I have no eyes, ears, tongue, or nose.
Yet I see, hear, taste, and smell everything.

What am I?

Question: My first two are male, and my first three female.
My first four save them both, and my whole is a female of the same sort.

What am I?

Question: Light hides me and darkness kills me.

What am I?

Question: I am a big threat to humanity,
but you wouldn't get rid of me even if you could.

What am I?

Question: At the end of a long dark cave there is a monster made of lead. Be careful. One twitch of the finger and you will release it.

What is it?