Can't we use 'get on' instead of 'come on', what's the defference between them?

Business English Courses, Elementary Level

ESL/EFL Test #19 [color=blue]“Late Again”, question 6

Or what? on, tell me.

(a) Get
(b) Come
(c) Take
(d) Put

Business English Courses, Elementary Level

ESL/EFL Test #19 [color=blue]“Late Again”, answer 6

Or what? Come on, tell me.

Correct answer: (b) Come
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Can’t we use “get on” instead of" come on" , what’s the defference between them?

‘Get on’ is not idiomatic-- we might use ‘Get on with it’, but that is rude, not persuasive.