Pyramid is to triangle as cube is to square. This relationship shows dimension. The triangle shows one dimension of the pyramid; the square is one dimension of the cube.
Toothbrush is to toothpaste as butter knife is to butter. This relationship shows function. The toothbrush is used to apply the toothpaste to teeth; the knife is used to apply butter to bread.
Hose is to firefighter as needle is to nurse. This relationship shows the tools of the trade. A hose is a tool used by a firefighter; a needle is a tool used by a nurse.
A U.S. flag is to a fireworks display as a Halloween mask is to a pumpkin. This relationship shows symbols. The flag and fireworks are symbols of the Fourth of July. The mask and pumpkin are symbols of Halloween.
The United States is to the world as a brick is to a brick house. This relationship shows part to whole. The United States is one part of the world; the brick is one part of the house.