What can you catch but never throw?

There is something which is always coming but never arrives?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Can anyone tell me a word in the English dictionary which has a silent 'z'?

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

It is always ahead of me yet I can never see it. What is it?

A fresher was sitting in an interview. The interviewer said, "This is the last question of your interview. Tell me the accurate position of the centre of this table where your resume is kept."

How can he answer this question? What will you have answered to such a question?

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