大型重要预应力构件，混凝土强度应达到设计强度的多少时，方能张拉预应力筋()
A.70%
B.80%
C.90%
D.100%
参考答案：D
The settlement is home to nearly 1,000 people, many of（）left their village homes for a better life in the city.
A. whom
B. them
C. which
D. those
变压器音响发生异常声音可能是什么原因？
