заполните смысловые пропуски в тексте соответствующими словамиTOOLS THROUGH THE AGESThe first knives were made about two and a half million years ago, they were crafted by early ancestors of modern humans. At first, пустоsharp pieces of stone were broken off a rock, but in later times they were sharpened and straightened into blades.The abacus is one of the first mechanical counting пустоdevices , an ancestor of today’s computers. It consisted of a frame containing beads on wires. The modern abacus was designed by the Chinese around the year 1200.The compass allowed sailors to navigate across oceans and пустоdiscover new worlds. The compass was invented by the Chinese about 2200 years ago. A spoon-shaped piece of magnetic rock was balanced on a flat пустоsurface . Since it was magnetic, the handle rotated to align itself with the Earth’s magnetic poles.The first mass-produced pencils were made in Germany in 1662, which helped writing and education to develop. The harness lets people control horses and пустоattach them to carts. It was probably invented about 6000 years ago, when horses were first tamed and kept. The scythe allows people to cut grass and harvest crops from the field. It consists of a long wooden пустоshaft with handles on the end and in the middle, and a long curved blade on the other end. The blade is sharp on the inside. It was first used in Europe in the 12th century.Glasses (or spectacles) make workers more productive and accurate, and allow people to work into old age. Mathematical calculations for a spherical lens were first made by Arab scientists in the 11th century. The first spectacles were manufactured by Italian пустоcraftsmen in the 13th century.Saws were first used by the Egyptians more than 5000 years ago to cut both wood and stone. They were made of copper. The first balance scales were seen in southern Mesopotamia about 9000 years ago. They consisted of two weighing pans attached to either end of a beam, which was balanced on a central пустоpivot . They allowed merchants to calculate the exact weight of goods.The chisel consists of a long, narrow, sharpened edge attached to a handle. It’s different from a knife or axe, because it is driven by a sharp blow from a hammer or пустоmallet . The earliest chisels were made from flint (a kind of stone) 10,000 years ago. Later they were used by the Egyptians to пустоcarve stone for the pyramids.