所以A并没有错，只是因为C是原版书定义所以选C？

问题如下：

The full employment, or natural, level of output is best described as:

选项：

A.

the maximum level obtainable with existing resources.

B.

the level at which all available workers have jobs consistent with their skills.

C.

a level with a modest, stable pool of unemployed workers transitioning to new jobs.

解释：

C is correct.

At the full employment, or natural, level of output the economy is operating at an efficient and unconstrained level of production. Companies have enough spare capacity to avoid bottlenecks, and there is a modest, stable pool of unemployed workers (job seekers equal job vacancies) looking for and transitioning into new jobs.

考点：充分就业

解析：充分就业时的产量不一定是最大的，但是是可以维继的。所以A选项不正确。

充分就业时依然会存在摩擦性失业和结构性失业，所以B选项错误。

C选项是原版书表述，充分就业时参与培训和寻找新工作的人都是很少的，并且是稳定的。