阅读下面短文，并根据短文后的要求答题(请注意问题后的字数要求)。
Modern inventions have speeded up people's lives amazingly．Motor cars cover a hundred miles in little more than an hour，aircraft cross the world inside a day，while computers operate at lightning speed．Indeed，this love of speed seems never ending．Every year motor cars are produced which go even faster and each new computer boasts(吹嘘)of saving precious seconds in handling tasks．
All this saves time，but at a price．When we lose or gain half a day in speeding across the world in an airplane，our bodies tell us so．We get the uncomfortable feeling known as jet lag； our bodies feel that they have been left behind in another time zone．Again，spending too long at computers results in painful wrists and fingers．Mobile phones also ，according to some scientists；too much use may put harmful radiation into our brains，a consequence we do not like to think about．
However，what do we do with the time we have saved? Certainly not relax，or so it seems．We are so accustomed to constant activity that we find it difficult to sit and do nothing or even just one thing at a time．Perhaps the days are long gone when we might listen quietly to a story on the radio，letting imagination take us into another world．
There was a time when some people's lives were devoted simply to the cultivation(耕耘)of the land or the care of cattle．No multi tasking there；their lives went on at a much gentler pace，and in a familiar pattern．There is much that we might envy about a way of life like this．Yet before we do so，we must think of the hard tasks our ancestors faced：they farmed with bare hands，often lived close to hunger，and had to make tools from wood and stone. Modern machinery has freed people from that primitive existence.
76．What's the passage mainly about?(within 10 words)
77．List the difficulties our ancestors met according to the text．(within 15 words)
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78．Fill in the blank in the 2nd paragraph with proper words or phrases．
79．Why do we make new products more and more time-saving according to Paragraph 1 of this passage?
80．Translate the underlined sentence in the 3rd paragraph into Chinese．