Option a is the correct answer. Nagabhata I founded the Gurjara-Pratihara dynasty around 730 CE, ruling northern India from Ujjain. He repelled an Arab invasion and expanded his control over the Avanti region. He was defeated by Rashtrakuta ruler Dantidurga but potentially regained power afterward. His legacy includes military achievements, disputed connections in inscriptions, and the Gurjara-Pratihara title, though rulers may not have been from the Gurjara tribe.