Final answer:
The handheld gaming system 3DS has allowed Nintendo to maintain its position as the top seller in the handheld-device industry.
Step-by-step explanation:
The 3DS, a handheld gaming system, has revolutionized handheld gaming and allowed Nintendo to remain number one in sales in the handheld-device industry.
The correct answer to this question is c) Nintendo. Sony, Microsoft, and Apple have all been engaged in the gaming market as well, but when it comes to handheld devices, Nintendo has been a dominant player, especially with the success of the 3DS platform which features 3D graphics without the need for special glasses, among other innovations.