What's the difference between tone and voice?

[Ecaterina]

Business Idiom in English, Intermediate level

ESL/EFL Test #63 "How to agree", question 6

I'm pleased to say that we speak on this matter with one ..........

(a) sound
(b) tone
(c) harmony
(d) voice

Business Idiom in English, Intermediate level

ESL/EFL Test #63 "How to agree", answer 6

I'm pleased to say that we speak on this matter with one voice.

Correct answer: (d) voice
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We say in one 'tone' but with one 'voice', I supose, don't we?

[Mister Micawber]

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Here, the idiom is 'with one voice', which means 'all in agreement'-- we all express the same opinion.
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Native English teacher at Mister Micawber's