∵a⊥b，∴a•b=1×（-2）+2k=0，解得k=1．
∴实数k的值为1．
故答案为1．
某带壁柱砖墙及轴向压力的作用位置如图，设计时轴向压力的偏心距e不应小于：（）
A.161mm
B.193mm
C.225mm
D.321mm
Americans eat _____ as they actually need every day. [ ]
A. twice as much protein
B. twice protein as much twice
C. twice protein as
D. protein as twice much
