What means "keep out"?

[Antey]

English Idioms and Expressions, Elementary Level

ESL/EFL Test #6 "Out of Control", question 8

There's a big notice up there which unfortunately we didn't see because it said 'out of bounds'.

(a) keep through
(b) keep out
(c) keep on
(d) keep in

English Idioms and Expressions, Elementary Level

ESL/EFL Test #6 "Out of Control", answer 8

There's a big notice up there which unfortunately we didn't see because it said keep out.

Correct answer: (b) keep out

Your answer was: correct
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What means keep out?

Antey

[Mister Micawber]

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Here, keep out means remain outside the boundary, do not enter, do not trespass, because the area is 'out of bounds'.
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Native English teacher at Mister Micawber's

[Baubau]

This sentence is from Alice in Wonderland, isn't it?