The comma tells us when to pause while reading and helps organize writing. Since commas can be used in a variety of ways, they have a few rules you must memorize.
In the given sentence, the following rule applies:
Use a comma in a personal title:
My mother’s name tag says Joan Smith, R.N.
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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.