Gravitational attraction exists between all objects in the universe. Which word, if any, should replace "all" in this statement to make the statement true.

any two

Explanation:

Gravitation force or gravitational attraction is a force of pulling or attraction that exist  between any two bodies that have a mass. Each and every body attract each other with the force of gravity due to their masses.

Every object in this universe having mass and distance attracts every other object.

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements