The answer is option A (Anglo-Saxon period).
Explanation:
The Anglo-Saxons were a tribe made up of three peoples (the Saxons, the Angles, and the Jutes). They invaded England after the Roman occupation and became the ancestors of the English people.
The Anglo-Saxons spoke Old English from which irregular verbs come from. We say the irregular verbs are native because they existed in Old English.
Irregular verbs change their form when conjugated in different tenses, for example, "begin" (began, begun) and "think" (thought).
