Answer:
A. coordination problem under central planning.
Step-by-step explanation:
In an economy under a central planning, All of the goods and services that should be produced in the country is fully controlled by the government.
This make it really impossible to achieve.
Citizens are inherently different and tend to have different needs in order to be satisfied in their life. Under the free-market system, these needs will be met through the power of supply and demand. AS long as enough people need it, there will always a producer who want to supply the product.
Under a central planning, this will create a coordination problem. There is now way for the government too ask the citizens one by one about what goods and services they need.