The meaning and the usage of the word "mirage"

[Dongocan]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #573 "Weather Test (10)", question 3

A ......... is an illusion or manifestation of something unattainable or greatly desired that appears to people who are in areas of hot areas. This happens because intense, hot air distorts the appearance of objects that are far away.

(a) mirage
(b) knot
(c) sandstorm

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #573 "Weather Test (10)", answer 3

A mirage is an illusion or manifestation of something unattainable or greatly desired that appears to people who are in areas of hot areas. This happens because intense, hot air distorts the appearance of objects that are far away.

Correct answer: (a) mirage

Your answer was: incorrect
A sandstorm is an illusion or manifestation of something unattainable or greatly desired that appears to people who are in areas of hot areas. This happens because intense, hot air distorts the appearance of objects that are far away.
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i can't undestand the meaning and the usage of the word "mirage"? could u explain more 2 me!many thanks 2 u! :-)

[Mister Micawber]

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A mirage is that area of unclear, wavering images that you can see at a distance in a flat, hot area. Some people think it looks like a distant body of water.
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Native English teacher at Mister Micawber's