My life is an open vault. vs My life is an open book.

[Mendy]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #546 "English Slang Idioms (149)", question 3

When asked if he minded recounting how he came upon the knowledge that allowed him to revolutionize the prosthetics field when he had no apparent medical training or schooling in biomechanics, he replied, "Not at all. My life is an open .........."

(a) account
(b) book
(c) vault
(d) door

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #546 "English Slang Idioms (149)", answer 3

When asked if he minded recounting how he came upon the knowledge that allowed him to revolutionize the prosthetics field when he had no apparent medical training or schooling in biomechanics, he replied, "Not at all. My life is an open book."

Correct answer: (b) book

Your answer was: incorrect
When asked if he minded recounting how he came upon the knowledge that allowed him to revolutionize the prosthetics field when he had no apparent medical training or schooling in biomechanics, he replied, "Not at all. My life is an open vault."
_________________________

why not open vault? aint there such idioms?

[Mister Micawber]

.
No, there is no such idiom. 'Ain't' is not a very educated word, either.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber