These nations are in the early stages of industry and technology.

a. unitary systems

c. developing nations

b. federal systems

d. developed nations

Since we're talking about nations, it is likely that the answer itself will also have the word "nations" in it: so let's look at the options c. and d.

They are only in early states, and it is assumed that they will develop further.

Therefore the correct answer is "c., developing nations".