What does 'on your marks' mean?

[Stupy]

English Idioms and Expressions, Advanced Level

ESL/EFL Test #25 "Mark Idioms", question 10

Pay attention. The race is about to begin. On your marks, get ready, start.

(a) Try prepared
(b) Act prepared
(c) Be prepared
(d) Go prepared

English Idioms and Expressions, Advanced Level

ESL/EFL Test #25 "Mark Idioms", answer 10

Pay attention. The race is about to begin. Be prepared, get ready, start.

Correct answer: (c) Be prepared
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More example please. for this expression..thanks

[Beeesneees]

In Britain, we often say 'On your marks, get set, go' at the start of a race. I presume this is an equivalent statement to that:
Be prepared/On your marks: take up the appropriate place on the starting line.
Get ready/get set: Tense your muscles into the appropriate stance to begin.
Start/go: run!
The usage of the phrase here is idiomatic.

More literal usage examples:
"She was asked if she would be prepared to read in church."
"In order to be prepared for the climb, the mountaineer trained on smaller slopes."
"Be Prepared" is the Boy Scout Motto. When Baden-Powell was asked, "Be prepared for what?" He said "Why, for any old thing."
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Cheers m' dears!