What goes up but never comes down?

I know a ten-letter word in the English language which can be typed using only the top rows of the computer keyboard.

Name the three-letter word that can complete the below words?

A) L O _ _ _ E
B) E D U _ _ _ E
C) _ _ _ E R
D) _ _ _ T L E

What has 88 keys?

Let's play a word game. Following are some meaningless words that can be completed by adding random letters on either side of the word.

For example, the word "rdo" can be formed into "pardon".

Using the same technique, can you complete the given words?
ecalc
airb
rinci
tibac
uidel
gorit
igna
eyho

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

What runs around the whole yard without moving?

What can you catch but never throw?

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

I am not alive, but I grow; I don't have lungs, but I need air; I don't have a mouth, but water kills me. What am I?