The best and most correct answer among the choices provided by the question is the first choice "<span>The Rus established a strong trading relationship with Constantinople."
</span>A monarchy formed in Kiev, and the Kievan Rus came into being. ... Contact and trade between Kiev and Constantinople increased. Kiev became a major trading hub in eastern Europe, and other than tangible goods, religion from the Byzantine Empire <span>found its way into Kiev.</span>
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It led to the fall of the Achaemenid Empire and gave Alexander room to expand eastward.Hope this helps.