The East India Company (EIC) utilized several tactics to monopolize trade in India. Among the options you've listed, the most relevant tactics employed by the EIC included:
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Loans and military support to local nawabs in exchange for trade compromises: The EIC often allied with local rulers (nawabs) and provided them with military assistance or loans in return for favorable trade agreements or concessions.
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Exclusive use of British soldiers to prevent local Indians from being armed: The EIC maintained a military presence in India, using British soldiers to suppress local uprisings and to ensure that they retained control over trade routes and key areas.
Although the EIC did engage in military actions and territorial expansion to secure trade and resources, the specific tactic of "invasion of the interior regions of India" is somewhat broad. The EIC did expand its control into India, but it did so in a manner that often involved alliances and administrative control rather than outright invasions.
The creation of port cities that allowed European nations to freely trade in the region is inaccurate in the context of the EIC's objectives, as it sought to restrict trade to its own operations rather than promoting free trade.
In summary, the EIC's key strategies included alliances with local rulers and military control to maintain their monopoly over trade.