Step 1: Understanding the Concept:
This question tests basic knowledge of English history, specifically the event that marks the beginning of the Anglo-Saxon period.
Step 2: Detailed Explanation:
Historical accounts, such as those by the 8th-century monk Bede, record that around the year AD 449, Germanic tribes—the Angles, Saxons, and Jutes—began migrating to and invading the island of Britain. This event occurred after the withdrawal of the Roman legions and marks the start of the Anglo-Saxon settlement of what would eventually become England.
Step 3: Final Answer:
The Anglo-Saxons invaded Britain in AD 449. Therefore, option (A) is the correct answer.