I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

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.

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

What does the following BrainBat signifies?

ABCDEFGHIJKLMNOPQRSTUVWYZ

QQQQQQQQQQQQQQQQQQQQQQQQQ.

You knock a Table over in the library, and suddenly 20 eyes are looking at you.

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?

A man calls his dog from the opposite side of a river. The dog crosses the river without a bridge or a boat and manages to not get wet. How is this possible?

A man started to town with a fox, a goose, and a sack of corn. He came to a stream which he had to cross in a tiny boat. He could only take one across at a time. He could not leave the fox alone with the goose or the goose alone with the corn. How did he get them all safely over the stream?

I am the beginning of the end, and the end of time and space. I am essential to creation, and I surround every place. What am I?

How can you write nineteen in a manner that if we take out one, it becomes twenty?