Final answer:
The best fit for the passage is option (a), reflecting the historical use of military power by imperial nations and the allowance for some economic self-management within colonies, though this was rare and heavily supervised.
Step-by-step explanation:
The passage is discussing the nature of imperial rule and how imperial powers managed their colonies. When considering the options provided, we need to recognize that imperial powers rarely left colonies to govern themselves entirely, especially not in terms of allowing them to develop independent economic systems or political structures. The practice of imperialism was driven by the desire for economic gain, political control, and the establishment of cultural dominance. Among the given options, 'imperial nations using military power control' aligns with the historical context of imperialism, which often involved the conquest and direct administration of colonies. Therefore, the best completion for the passage would be option (a), as it reflects the imperial nations' use of military power and how, despite tight control, there might have been occasional allowances for colonies to establish their own economic systems, although this was not the norm and was tightly overseen by the imperial authority.