The best explanation for why Ivan IV created the oprichnina during his reign is:
**B. Ivan IV was struggling against the boyars and wanted to limit their power.**
The oprichnina was a policy implemented by Ivan IV (also known as Ivan the Terrible) in the 1560s that aimed to consolidate his power and suppress the nobility (the boyars) who opposed him. It involved the establishment of a separate territory and force loyal to Ivan, allowing him to exert greater control and eliminate potential rivals among the boyars.