What property of half-lives makes radioactive material so problematic? check all that apply?

I believe the best answer is both A and B, that is there is no known way to shorten a half life, radioactivity is limited by the natural decay-time to stable isotopes, and again all half-lives are long, there is no known way to measure half-lives are long, there is no known way to measure half-lives with any accuracy. Half life is the time taken by a radioactive material to undergo decay to reach half of its original mass. 

That result from subduction of oceanic plates beneath lighter continental plates. most of the earth's volcanoes are located around the pacific ring of fire because that the location of most of the earth's subduction zones.