What has many keys but can’t open a single lock?

Known by all without exception, Forever here, for your protection, Sometimes strong, sometimes weak, Right after the night I come - hot and chic. And while millions of miles away, I always get to you, I find my way. No life around could do without me, Can you guess what I might be?

You throw me out when you want to use me and you take me in when you don't want to use me.

Who Am I?

I have a head like a cat and feet like a cat, but I am not a cat. What am I?

What jumps when it walks and sits when it stands?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

There is a five-letter word which has 3 consonants(all are same) and 2 different vowels.
Also, something wrong is associated with the word.

Can you name it?

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

You can find some missing letters in the picture. By placing two particular letters in the spaces, you can form a nine lettered word beginning from one of the corners and going clockwise direction to the middle. Can you find out the letters and the word?

I make two people out of one. What am I?