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.

Direction: Read the following passages carefully and answer the question that follows.
An iron or steel bridge swells (gets larger) when warmed by the Sun and shrink (gets smaller) when it becomes colder. Heat makes everything expand and cold makes everything contract. Cold is the absence of heat. Metals change their size when heated or cooled and this change is noticeable in a bridge that is made of iron or steel. The builder of a bridge must leave empty spaces for the metal to expand into. Have you noticed that concrete sidewalks have cracks every few feet ? These cracks provide space for the concrete to expand into when heated.

Direction: Read the following passages carefully and answer the question that follows.
An ear of corn on a corn plant is protected by a husk and at the end of the ear, emerging from the husk, you can see a bunch of silk-like threads. What is the purpose of these threads ? Well, each thread is attached to a kernel of corn inside the husk and each kernel of corn, if it is fertilized by pollen, can become a seed that can grow into a new corn plant. How does pollen reach the kernel ? It travels through the silk-like thread, which is a hollow tube.