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- Ab extends by 2mm and bc contracts by 2mm .
- Soldiers of bad character were branded bc .
- Glass-making flourished as early as 1350 bc .
- The tube abc shown is cantilevered with ab and bc in a horizontal plan .
the vertical displacement =1mm is normal to the bars ab and bc and hence does not affect their length. 竖向位移1mm垂直于AB和BC，故不影响它们的长度。