71. Along the major riversthat traverse the deserts of northeast Africa, the Middle East, and northwest India,the combination of a reliable supply of water and good growing conditions both encouraged farming traditions that, in places, endure in at least 6,000years
(A) good growing conditionsboth encouraged farming traditions that, in places, endure in
(B) good growing conditionsencouraged farming traditions that have, in places, endured for
(C) of good growingconditions have encouraged farming traditions that, in places, endured for
(D) of good growingconditions both encouraged farming traditions that have, in places, endured
(E) of good growingconditions encouraged farming traditions that have, in places, been enduring for
疑问： 1、对于完成时的解释是一个动作发生在过去，已经结束但影响持续到现在，或者是动作一直持续到现在，所以在这个句子中，既然后面已经说了farming traditions that have endured for at least 6,000years 那么就是说明encourage的影响持续到现在了呀，是不是用完成时更好？
2、关于平行，个人觉得没有of是说的通的，但是有了of 这个句子变成the combination of a reliable supply of water and a reliable supply of good growing conditions 也应该可以吧，虽然前面修饰语有些多，不够简洁，但是语法上应该也是对的吧？