The hottest place in the world is the Sahara Desert in Africa. But there are deserts in many other places: in America, in Asia and in Australia. In 1917 the temperature in Death Valley, in the United States, was over 48°C every day for six weeks. That's very hot!But deserts are not always hot. After dark, deserts are very cold.
   Not many animals and plants can live in a desert, because it doesn't rain very often. But one animal likes the desert — the camel. It has big feet to walk on the sand. It can live for a long time without water. Sometimes it doesn't drink anything for weeks — so it gets very thirsty! When it finds water it can drink 100 liters(升) at a time.

有调查显示,“不愿降低身价”是近年来高校毕业生就业难的一个重要因素。但在各省市，许多大学生村官在新农村建设中升华了理想，实现了人生价值。这启示我们（  ）

①要立足实际，恰当定位          ②结合社会需要,实现成才目标

③在实践中实现自身价值          ④迫于就业压力,不得不当村官

分解因式： -12x⁴y+3xy