The fact "A sidewalk is usually made of concrete." is illustrated with the story:1. The sidewalk in front of my house was being repaired last week.2. The workmen tore up the old concrete with jackhammers.3. Concrete is a liquid mixture containing sand and cement, that becomes as hard as stone when it dries.4. My cat walked on the concrete while it was still wet.5. Many sidewalks in town have handprints, footprints, and people's initials, pressed into them.