What important strategy used by the Romans had the effect of unifying their empire? A Building a large transportation network of roads and bridges
B Using powerful navies to protect sea trade routes
C Supporting free-market economies by using silver coins
D Granting citizenship and voting rights to conquered peoples

A, building a large transportation network of roads and bridge

Explanation:

The romans used built roads to trade goods, education, religion and culture making Roman a diverse empire with different roads and bridges to make it mix society and influential.

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answer; oxygen to the brain;