What does 'to be with you on that' mean? I agree with you?

[Agreeer]

Business Idiom in English, Intermediate level

ESL/EFL Test #137 "Ways of agreeing", question 1

I'm certainly ......... you on that.

(a) on
(b) with
(c) by
(d) to

Business Idiom in English, Intermediate level

ESL/EFL Test #137 "Ways of agreeing", answer 1

I'm certainly with you on that.

Correct answer: (b) with
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to be be with you on somethingis to agree?

[Alan]

Hi,

In its broadest sense 'I'm with you' means I support you/I'm on your side and as you say, it means 'I agree with you'.

Alan
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English as a Second Language
You can read my ESL story The way you write it