Meaning of what on earth

[Thanya]

Test No. incompl/elem-28 "Responses", question 4

Mike: 'They went on strike last week.'
Jane: '.........'

(a) What on earth for?
(b) Are they on earth?
(c) Do they live on earth?
(d) Why on earth to?

Test No. incompl/elem-28 "Responses", answer 4

Mike: 'They went on strike last week.'
Jane: 'What on earth for?'

Correct answer: (a) What on earth for?

Your answer was: incorrect
Mike: 'They went on strike last week.'
Jane: 'Do they live on earth?'
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I dont know it doesnt mean? pls reply me.

[Alan]

This is a question you ask when you are very surprised that somebody has decided to do something which you don't understand. If someone says to you: I have decided to sell everything, buy a boat and sail round the world, you could be very surprised about this and say to that person: What on earth for? In other words what is the reason for your decision?
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English as a Second Language
You can read my ESL story Word Story: Jokes