Production－possibility frontier（PPF）生产可能性边界

概念题：技术前沿（technology frontier）

The pioneers _________ the frontier had a difficult life with few comforts.

On a production possibilities frontier, production is efficient if the production point is

中国大学MOOC: Leatherstocking Tales is a novel best-known for the frontier period.

France produces wine and tractors. If, given the same resources, France can increase production of wine and tractors, at the same time, then France A: is producing outside his Production Possibility Frontier B: is has achieved technological advancement in the production of kola and cashew nuts C: is producing on its Production Possibility Frontier D: is producing inside its Production Possibility Frontier

Many people are still _____________ by the frontier because it has been particularly important in________ _________________________________ .

People living on the frontier were _________ many society’s _________，they also _________ society’s ____________________________.

When Mark Twain became a miner in the frontier region, he started to write.

In the early frontier, which existed before the Civil War of the 1860s, the main struggle was man against the____________.