They can also learn about the history of tractors .

他们还能了解到拖拉机的历史。

Entry-level tractors cost around $ 4000 .

一辆基本配置的拖拉机售价约为4000美元。

But the advent of tractors and combine harvesters did not lead to permanent unemployment .

但拖拉机和联合收割机的出现并没有带来永久性的失业。

As news spread , the farmers raced into town on their tractors .

随着消息传开，农民们开着拖拉机跑进城里。

He says farmers in the developing world can use precision agriculture even without high-tech tractors .

他说发展中国家的农民也可以应用精准农业，即便没有高科技拖拉机。