Hint: From the second century BC, the Hunas occupied the borders of China. Hunas were a nomadic tribe who gathered power in the 5th century AD in Central Asia.
Complete answer: The Hunas entered India and occupied Gandhara in the northwest. Skandagupta was the first Gupta king to face the Hunas. He gave the Hunas a crushing defeat. This defeat stopped the Hunas from attacking India for the next fifty years. However they destroyed the empire of Persia and established their kingdom in the capital of Balkh.
The Gupta empire was disintegrating in the beginning of the sixth century AD. During this period Toramana continuously attacked the kingdom. Even though there is no confirmation to prove that Toramana was a Huna king, many people believed him to be one. This time the Hunas were successful in capturing Kashmir, Punjab, Rajasthan, parts of Uttar Pradesh and Madhya Pradesh. Toramana became weak at the end of his reign. He lost most of his indian territories. In 515 AD Toramana was succeeded by his son Mihirakula. Mihirakula was an ambitious ruler who made Sialkot his capital. The Hunas succeeded in their further invasions.
Hence, Option A is the right answer.
Note: The Gupta empire came to an end in 550CE because of a series of weak rulers and repeated invasions from the east, west and north. The success of the Hunas in India was not everlasting. The credit goes to Skandagupta for checking their advances when they were most powerful.