• necessary ⪢⪢
If something is _____ , you must do it.
http://qindex.info/i.php?x=13921

• necessary ⪢⪢
It is necessary to have a passport when you travel to a foreign country.
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◎◎◎ essential ⪢⪢
If something is _____ , it is very important and necessary.
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◎◎◎ protein ⪢⪢
_____ is a substance that is necessary for the body to grow and be strong.
http://qindex.info/i.php?x=13535

• 01 Introduction to Mathematics
○ Many students wonder why it's even necessary to learn in the first place. ○ How social media knows who you're going to tag in a photo before you do.
http://qindex.info/i.php?x=4817

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