signs for "in"
inside = “in”
location reference = pointing 
non-inside source = eliminate “in”
come in = enter

examples
inside vs location reference
Their food is in the car. (inside) 
Their food is in the kitchen. (location reference) 

non-inside source 
I live in America. 
I was born in 2000.
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enter (get in, come in)
They got in the house.