Final answer:
Ender practiced with Petra and the Launchies because Bonzo Madrid, the commander of the Salamander Army, forbade him from joining the army practice sessions due to animosity.
Step-by-step explanation:
Ender practiced with Petra and the Launchies because Bonzo wouldn't let him play in the army practice sessions. The correct answer to the question is A. Bonzo. In Orson Scott Card's novel 'Ender's Game', Bonzo Madrid is the commander of Salamander Army, who takes an instant dislike to Ender Wiggin. Due to Bonzo's animosity and jealousy, he forbids Ender from participating in the army's practice sessions, prompting Ender to find alternative ways to improve his battle skills. This leads Ender to practice with Petra Arkanian, one of the few friends and allies he has during his early time at Battle School, and the other new recruits, referred to as Launchies.