Anthropologists are scientists that study people who often lived hundreds or even thousands of years ago. Items those men, women, and children left behind when they died --- everything from clothing to jewelry and tools --- tell anthropologists a lot. And sometimes even their words survive.     Experts believe that a discovery in Mexico is the oldest example of writing ever found in the Americas. The people who created it probably lived 3,000 years ago, long before Christopher Columbus arrived in the New World.     Workers digging in a rock mine happened to notice a stone block with marks carved onto its surface. They found the large piece of stone near the city of Cascajal, Mexico, which was once the capital of an ancient people called the Ohmec.     "There are signs on the block that seem to show objects used by the Olmec during their religious ceremonies," says Dr. Stephen Houston, of Brown University in the USA. "There is a sign that looks very similar to a knife and another that looks like the chair of a King," he explains.     Houston, an expert on the writing systems of ancient cultures, says the discovery is exciting because "it makes clear that the Olmec could read and write. It is like hearing voices from the past."     But experts don't know exactly what the writing says. Finding other examples of Olmec writing could help decipher the puzzle.     "We could have whole sets of ancient writing which will basically make ancient people speak to us directly," says Houston. "There are many puzzles to be solved, and this is just one of them." According to the passage, what items do scientists often use to learn more about the past?
Clothing and jewelry. Books and stones. Knives and chairs. People and animals.