Why we have to use "which" in this sentence?

[Alex Anna]

English Grammar Tests, Elementary Level

ESL/EFL Test #93 "Why Questions", question 8

......... Caribbean island does Sir Vivian Richards come from?

(a) Which
(b) What
(c) Where
(d) Who

English Grammar Tests, Elementary Level

ESL/EFL Test #93 "Why Questions", answer 8

Which Caribbean island does Sir Vivian Richards come from?

Correct answer: (a) Which

Your answer was: incorrect
Where Caribbean island does Sir Vivian Richards come from?
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I dont know why we have to use "which" in this sentence?

Alex Anna

[Alan]

Hi,

Interrogative 'which' is used here to indicate that the question is asked about the particular island he comes from.

A
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English as a Second Language
You can read my ESL story Word Story: Jokes