磁制冷主要应用极低温和液化氦等小规模的装置中．虽然诸多原因的限制，使磁制冷基础理论尚未成熟，但磁制冷终将因其高效、无污染等特点成为未来颇具潜力的一种新的制冷方式，而对磁制冷循环理论的拓深必能大力推进磁制冷技术在太空开发和民用技术中的应用，为磁制冷开辟更加广阔的前景．

     19﹣20世纪，冰箱和空调最常用的制冷技术是使用氟利昂制冷（如图1）．通过对氟利昂的蒸发和液化，来降低冰箱箱体内的温度，从而达到制冷目的．但是氟利昂中的氯氟烃释放到大气中经太阳照射作用，会破坏臭氧层，且连续反应，一个氯分子可破坏一万个臭氧分子，而臭氧层为保护地球上的生物免受过多紫外线照射起到了重要作用．为了保护臭氧层不被破坏，需要寻找一种无害的新型制冷技术．

      某些磁性材料磁化时会放出热量，退磁时会吸收热量，这个过程称为磁热效应（见图2），如果让这种效应持续进行，就能得到理想的低温，利用这种方式制冷称为磁致冷技术．

请根据上述材料，回答下列问题：

D

    How old is "old"? The answer has changed over the years. Two Hundred years ago, you were old at 35. At the beginning of the 20th century, the average life span(平均寿命) was 45. In 1950, 70-year-olds were really old. Today, a healthy 70-year-old is still thought young.

    So, how old is "old"? The answer is one you've heard many times, from all kinds of people. "You are as old (or young) as you feel. " Your age simply tells you how many years you have lived. Your body tells you how well you've lived.

    "Nobody grows old by living a number of years, "Wrote a writer. "People grow old when they don't have their ideals(理想)." People shouldn't have the wrong ideas about aging. Sometimes, older minds can be as bright as young minds. Alice Brophy once said, "It makes me unhappy when people say, 'You look young for your age.' What does that mean? You know you can die old at 30 and live young at 80."

如图，在Rt△ABC中，AB=CB，BO⊥AC，把△ABC折叠，使AB落在AC上，点B与AC上的点E重合，展开后，折痕AD交BO于点F，连接DE、EF．
下列结论：①tan∠ADB=2；②图中有4对全等三角形；③若将△DEF沿EF折叠，则点D不一定落在AC上；④BD=BF；⑤，上述结论中正确的个数是（　　）

“鸟类的黑手党”﹣﹣杜鹃，将自己的卵产到别的小鸟巢中，小鸟辛勤地为杜鹃孵卵并精心喂食杜鹃的雏鸟．对小鸟这种行为的解释，正确的是（　　）

①是先天性行为     ②是学习行为     ③是生殖行为     ④是觅食行为

⑤是由遗传因素决定的     ⑥是防御行为     ⑦是由环境因素决定的．