Can you find the missing piece of the Porsche?

The more you take me, the more you leave me behind.
Who Am I?

What has one letter and starts with an E?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

The dirtier I get, the whiter I look. Who am I?

If a wheel has 54 spokes, how many spaces are there between the spokes?

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.

During which month do people sleep the least?

This is a most unusual paragraph. How quickly can you find out what is so unusual about it? It looks so ordinary, you'd think nothing was wrong with it. Actually, nothing IS wrong with it. But it is not as ordinary as you might think. If you think about it for a bit, you will find out why it is truly so unusual. So what is it? What is so unordinary about this paragraph?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?