Ultraviolet rays are absorbed by water in the atmosphere not absorbed by water in the atmosphere slowed down by water in the atmosphere rendered harmless by water in the atmosphere

A material’s radioactivity cannot be changed by altering the material physically.

Explanation:

Marie Curie studied the radiation of all compounds containing the known radioactive elements. She discovered that:

- The strength of uranium radiation can be exactly measured;

- The intensity of radiation is proportional to the amount of the radioactive element;

- The ability to emit radiation depends only on the interior of the atom, so it doesn't depends on the material physically.