填空题

Technological invention has directly or indirectly produced social change in every period of history. The invention of the horse collar in the Middle Ages was a (36) technological advance for agriculture; the (37) for use at sea so (38) navigation in the fifteenth century that it led in the age of (39) ; and the steam engine was an (40) factor in the industrialization of Europe in the nineteenth century. A discovery is another kind of technological (41) . While inventions add something new to a culture, discoveries (42) our knowledge of something that already exists. Gravity had always been there, but Newton "discovered" it: he (43) .how this natural from worked and how its laws applied to falling bodies. This knowledge made possible many new inventions. (44) . Since each invention makes more inventions possible, the speed of technological development tends to accelerate. Benjamin Franklin experimented with electricity in the eighteenth century, (45) . In the hundred years since Edison invented the light bulb, the discovery of electricity has led to tens of thousands of inventions, from the internal burning engine to the computer. (46) pose some of the greatest challenges of our time.