C. A nation is protected by an imperial power in return for trade privileges.
An example of sphere of influence can be found in China, in which the US, Britain, Russia, France, etc. etc. gained their spheres of influence through helping to put down the boxer rebellion, and gaining lands that they could "influence" (hence the name). An example can be found in Hong Kong, in which Britain has their "influence", and is reflected through the government and how the country runs.
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