Respuesta :

[tex]Associative\ property:a+(b+c)=(a+b)+c\\\Downarrow\\2+(8+9)=(2+8)+9\\\\Your\ answer:\huge\boxed{D.\ associative}[/tex]
Its the Associative property which is a + (b + c) = ( a + b ) + c

So its your option D
associative property