What does this rebus means ?

PROG WORKRESS

What does this simple rebus mean?

What happened when the wheel was invented?

How many times can you subtract the number 5 from 25?

I have a head like a cat and feet like a cat, but I am not a cat. What am I?

Only one colour, but not one size,
Stuck at the bottom, yet easily flies.
Present in sun, but not in rain,
Doing no harm, and feeling no pain.
What is it?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

Count the number of balls in picture below:

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