What does break open mean?

[Yantra]

English Language Tests, Intermediate level

ESL/EFL Test #148 "Idioms with the phrasal verb break", question 6

"Be careful not to spill the yolk when you ......... the egg."

(a) break out
(b) break off
(c) break open
(d) break down

English Language Tests, Intermediate level

ESL/EFL Test #148 "Idioms with the phrasal verb break", answer 6

"Be careful not to spill the yolk when you break open the egg."

Correct answer: (c) break open
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why?

[Mister Micawber]

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Why what? Each verb phrase has a different meaning, which you can find HERE.
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Native English teacher at Mister Micawber's