Occurred vs. happened?

[Nicol]

Test No. incompl/inter-65 "How to ask a question", question 9

What has ......... to your New Year resolution to stop smoking?

(a) occurred
(b) fallen
(c) happened
(d) occasioned

Test No. incompl/inter-65 "How to ask a question", answer 9

What has happened to your New Year resolution to stop smoking?

Correct answer: (c) happened

Your answer was: correct
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I would be most interested to know Why "occured" doesn't fit?
Many many thanks friends

[Alan]

Occurred would be wrong here because it is not used in the sense of what has gone wrong with or happened to.
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