Final answer:
Productively efficient in an economy indicates the use of the least costly production techniques to produce goods, utilizing all resources in such a way that no additional output can be achieved without trade-offs.
Step-by-step explanation:
If an economy is being "productively efficient," then it means that the economy is using the least costly production techniques to produce goods.
Productive efficiency is a concept in economics where all available resources are employed so that it is impossible to produce more of one good without decreasing the quantity produced of another good.
This efficiency is represented on a production possibilities frontier (PPF) where any choice like B, C, and D on the curve indicates productive efficiency, demonstrating that all resources are efficiently used and none can be reallocated to produce more without trade-offs.