what is an advantage of a command economy?
a. ability to make changes is slow and controlled
b. all the means of production are owned by the people
c. the military controls the economy through force
d. ability to make major changes in a short period of time

D. ability to make major changes in a short period of time

Explanation:

While other options are can be true of a command economy in certain situations, option D is the only option that I would classify as an advantage of a command economy over a Market Economic System. However, major changes in a short time can have disastrous consequences, for example the 6-7 million deaths that resulted from Stalin's five year plan.

they united the colonies in their fight against the british.

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.