在下面一段文字横线处补写恰当的语句，使整段文字语意完整连贯，内容贴切，選辑严密。每处不超过10个字。

    自第一颗人造地球卫星进入太空以来，除了载人航天飞行器会回收以外，其它上天的人造物体陆续被遗弃在太空中，①____。太空垃圾已经威胁到人类的航天活动。比如厄瓜多尔的一颗卫星升空后不到一个月，就与太空中的火箭残骸相撞而报废。这种威胁不仅仅发生在太空，甚至地球上的人类生活也会②____。因此，③____，应是人类接下来要解决的一个重要课题。

估算．

①“三个代表”重要思想是立党之本、执政之基、力量之源

②“三个代表”重要思想是指引全党、全国人民为实现新世纪新阶段的发展目标而奋斗的根本指针

③“三个代表” 重要思想是面向21世纪的中国化的马克思主义

④“三个代表”重要思想同马列主义、***思想、邓小平理论一道，是我们党和国家必须长期坚持的指导思想

   The Japanese Macaca monkey has been studied in the wild for over 50 years. In 1952, on one small Japanese island, scientists dropped some 1  in the dirt for the monkeys. The monkeys liked their taste, but they found the dirt  2.
   One clever 18-month-old monkey found she could 3 the problem by washing the sweet potatoes in a nearby river. She taught this to her mother. Her 4 also learned this new way and they taught their mothers, too.
   All the younger monkeys 5 learned to wash the dirty sweet potatoes to make them 6 to eat. But many old monkeys found it very hard to learn this and still ate the 7 sweet potatoes.
   Then something very surprising 8. In the autumn of 1958, scientists found that the monkeys on other nearby 9 began washing their sweet potatoes too. Scientists still don’t fully understand how this knowledge was 10 from one island to another.