What goes up but never comes down?

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

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

If there are fifteen crows on a fence and the farmer shoots a third of them, how many crows are left?

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?

What can you catch but never throw?

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

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

There are 2 cops parked along a one-way street looking for traffic violations. They spot a taxi driver going in the wrong direction, yet they do nothing.

Why?

What has 88 keys?