Answer :

That is because two itself is an even number. Also, if you add two to any even number it will always result in an even number. Therefore, every even number is a multiple of two.
Because 2 is always a start of an even number, so people use that as a reference to keep going, counting even numbers. Because since 1 is always the start of every number (odd wise), then they use that to sometimes count odd numbers, so just like one, 2 can be a reference.

If it's confusing then sorry, but I tried. Hope that helped :)

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