'away on business' vs 'away for business'

[Dima]

Business Idiom in English, Intermediate level

ESL/EFL Test #53 "Business Expressions (2)", question 6

I'm afraid it won't be possible to talk to the boss today because he's away ......... business till Tuesday.

(a) off
(b) on
(c) for
(d) to

Business Idiom in English, Intermediate level

ESL/EFL Test #53 "Business Expressions (2)", answer 6

I'm afraid it won't be possible to talk to the boss today because he's away on business till Tuesday.

Correct answer: (b) on

Your answer was: incorrect
I'm afraid it won't be possible to talk to the boss today because he's away for business till Tuesday.
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why is it wrong?

Dima

[Alan]

Hi,

'On business' suggests that you are away dealing with business. 'For business' would sound strange on its own and would more likely be something like 'for business reasons'.

Alan
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English as a Second Language
You can read my ESL story 'the' vs. 'a/an'