Central planning is used primarily in a
a. market economy
b. social economy
c. command economy
d. traditional economy

Central planning is used primarily in a command economy - c.

In a command economy you have the state which dictates the general flow of the goods which also means the state has to create central planning in order to be able to determine the flow of goods and the distribution how nad where it will go. 

2. is bettergo with that