What does "sticking his neck out" mean?

[Mickey]

English Language Tests, Intermediate level

ESL/EFL Test #242 "A Sticky Moment", question 6

He was rather sticking his neck ......... because Andrew had in fact once been a police officer.

(a) through
(b) over
(c) to
(d) out

English Language Tests, Intermediate level

ESL/EFL Test #242 "A Sticky Moment", answer 6

He was rather sticking his neck out because Andrew had in fact once been a police officer.

Correct answer: (d) out

Your answer was: correct
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What does "sticking his neck out" mean?

[Mister Micawber]

Taking a risk.
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Native English teacher at Mister Micawber's