The job or function of a word is what gives the label for its part of speech. English has eight parts of speech which are:
A preposition is a word that precedes a noun or pronoun to show its relationship with another word in the sentence.
The book is on the table.
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The correct answer is
The smallest number is the one that comes first while counting.
To arrange the given numbers in order from smallest to greatest, find the smallest number among all the given numbers.
21 is the smallest number.