The flag of Nepal is not rectangular.
Why it is true
It is the only non-quadrilateral national flag, featuring the shape of two overlapping pennants, representing the Himalayas.
Source: Geography
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This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.