Explanation:

From the decline of the Guptas until the rise of Harshavardhana in the early seventh century, several kingdoms emerged and held power in various parts of Northern India. Let's consider each option:

1. The Guptas of Magadha: After the decline of the main line of Guptas, some later Guptas still managed to hold on to parts of Magadha for some time.

2. The Paramaras of Malwa: The Paramaras rose to prominence much later, in the 9th to 14th centuries, so they wouldn't fit in the period immediately after the decline of the Guptas.

3. The Pushyabhutis of Thanesar: This dynasty did hold power in the region of Thanesar, and Harshavardhana himself belonged to this dynasty.

4. The Maukharis of Kanauj: The Maukharis ruled in the region of Kanauj before the rise of Harsha.

5. The Yadavas of Devagiri: The Yadavas of Devagiri emerged much later, around the 9th century, and primarily held power in the Deccan region.

6. The Maitrakas of Valabhi: After the decline of the Guptas, the Maitrakas established their kingdom in the region of Valabhi and were prominent players in western India.

So, the correct kingdoms that held power in Northern India from the decline of the Guptas until the rise of Harshavardhana are: The Guptas of Magadha, The Pushyabhutis of Thanesar, The Maukharis of Kanauj, and The Maitrakas of Valabhi.

Thus, the correct answer is 1, 3, 4, and 6.