Sentence:  A tough test for even the strongest climber, it was new to the Tour de France this year, but its debut will be remembered for the wrong reasons after one of those spectators scattered carpet <WSD>tacks</WSD> on the road and induced around 30 punctures among the group of riders including Bradley Wiggins, the Tour's overall leader, and his chief rivals. 
Meaning of the word marked with <WSD> tags:  A small nail with a flat head.