Jawaban:

a. The USSR is a representative of communism.

b. The Americans are accustomed to a system of private enterprise.

c. To control an economy is much the same as to direct.

d. The work was carefully monitored by the authorities for five years.

e. It is necessary to make a sharp distinction between planned and unplanned economies.

f. He does not work in this sector of the economy but in the public one.

g. A mixed economy possesses some of the qualities of the two main forms of economic system.

h. Coal, steel and farming are very important national industries.

i. The majority of the workers were happy about the new plan, but a small number were not.

j. Some industrial firms, like BP and ICI, are international as well as national in their activities.

Note that the above words are used in the context of the text, but it's possible that in other context the same word could have a different meaning.