1. If x and y are real numbers, then xy is a/an______number. 2. x•y=__•x 3. x + (y + 2) = ___+z 4. x+y=y+___ 5. (xy)z=___(yz) 6. x(y + z) =___ +XZ 7. 0 +x= __' 8. X• 1 = 9. O is the___ element for addition. 10. If x - =1, where x + 0, then x and___are called reciprocals of each other.