保证石油天然气钻井安全的关键技术是什么？
参考答案：
井控技术。
若loga2＞logb2＞0，则a，b的大小关系是______．
So far this year we _____ a fall in house prices by between 5 and 10 percent. [ ]
A. saw
B. see
C. had seen
D. have seen
