Replace the highlighted word segment with the appropriate one-word substitute.…

To identify the correct one-word substitute for "government ruled by a small, powerful group," let’s analyze the definitions of each option provided:

Definitions of Government Systems
Oligarchy: A form of government in which power effectively rests with a small number of people, often distinguished by nobility, wealth, education, or corporate, religious, or military control. This matches the description "ruled by a small, powerful group."

Anarchy: A state of disorder due to absence or nonrecognition of authority; it implies no government at all.

Theocracy: A system of government in which priests or religious leaders rule in the name of God or a god.

Democracy: A system of government where the whole population or all the eligible members of a state participate in power, typically through elected representatives.

Conclusion
The correct one-word substitute is Oligarchy (Option 2).