Direction: Read the following passages carefully and answer the question that follows.
We know that gold and silver are elements. An element consists of atoms of only one kind, unlike water, which consists of both hydrogen and oxygen. Another element is radium. Radium is especially interesting, because it produces heat, When soil is carried by rivers down to the sea and falls to the bottom, it often carries radium in it. As more and more soil is washed down into the ocean. more and more radium is carried in it. There, as elsewhere, it constantly produces heat.