《阅读理解特训:3 真 2 模含解析》2014 届高三英语二轮突破 11C6[2013·重庆卷] CAlmost every machine with moving parts has wheels, yet no one knows exactly when the first wheel was invented or what it was used for
We do know,however,that they existed over 5,500 years ago in ancient Asia
The oldest known transport wheel was discovered in 2002 in Slovenia
It is over 5,100 years old
Evidence suggests that wheels for transport didn't become popular for a while, though
This could be because animals did a perfectly good job of carrying farming tools and humans around
But it could also be because of a difficult situation
While wheels need to roll on smooth surfaces, roads with smooth surfaces weren't going to be constructed until there was plenty of demand for them
Eventually , road surfaces did become smoother, but