为减少锚具变形引起的预应力损失，应该采取的措施是( )。
A．选择变形小的锚具
B．减少垫板的块数
C．选择较长的台座
D．A+B+C
参考答案：D
—David, is that man your Chinese teacher?
—It _______ be him. He's having a meeting. [ ]
A. mustn't
B. can't
C. needn't
D. won't
史官这一名称始出于（）
A.商朝
B.黄帝时期
C.尧时期
D.禹时期
