与土壤保水、保肥、通气、透水能力有关的主要因素是（  ）   

阅读下面材料，在空白处填入适当的内容(1个单词)或括号内单词的正确形式。

             A mong all the fast growing science and technology, the research of human genes, ____biological engineering as people call it, is drawing more and more attentionnow. Sometimes it is a hot topic ____(discuss) by people.

          The greatest thing that gene technology can do is to cure serious diseases thatdoctors at present can almost do nothing with, such as cancer and heartdisease. Every year, millions of people are murdered by these two ____(kill).And to date, doctors have not found ____ effective way to cure them. But if thegene technology ____(apply) , not only these two diseases can be curedcompletely, ____(bring) happiness and more living days to the patients, butalso the great amount of money people spent on curing their diseases can besaved, so ____ benefits the economy as well. In addition, human life span(寿命) can be prolonged.

         Gene   technology can help people to give birth to more healthy and clever children.Some families, with the English imperial(皇室)family being a good example, have hereditary diseases. This means theirchildren will for sure have the family disease, ____ is a great trouble forthese families. In the past, doctors could do nothing about hereditarydiseases, ____ gene technology can solve this problem ____(perfect). Thescientist just needs to find the wrong gene and correct it, and a healthy childwill be born.