Given the question: Information:  - A smartphone is a mobile phone (also known as cell phones or cell mobiles) with an advanced mobile operating system that combines features of a personal computer operating system with other features useful for mobile or handheld use. Smartphones, which are usually pocket-sized, typically combine the features of a mobile phone, such as the abilities to place and receive voice calls and create and receive text messages, with those of other popular digital mobile devices like personal digital assistants (PDAs), such as an event calendar, media player, video games, GPS navigation, digital camera and digital video camera. Smartphones can access the Internet and can run a variety of third-party software components ("apps" from Google Play, Apple App Store, etc). They typically have a color display with a graphical user interface that covers more than 76% of the front surface. The display is almost always a touchscreen and sometimes additionally a touch-enabled keyboard like the Priv/Passport BlackBerrys, which enables the user to use a virtual keyboard to type words and numbers and press onscreen icons to activate "app" features.  - A mobile device (or handheld computer) is a small computing device, typically, small enough to hold and operate in the hand and having an operating system capable of running mobile apps. These may provide a diverse range of functions. Typically, the device will have a display screen with a small numeric or alphanumeric keyboard or a touchscreen providing a virtual keyboard and buttons (icons) on-screen. Many such devices can connect to the Internet and interconnect with other devices such as car entertainment systems or headsets via Wi-Fi, Bluetooth or near field communication (NFC). Integrated cameras, digital media players, mobile phone and GPS capabilities are common. Power is typically provided by a lithium battery.   - iPhone is a line of smartphones designed and marketed by Apple Inc. They run Apple's iOS mobile operating system. The first generation iPhone was released on June 29, 2007; the most recent iPhone model is the iPhone 7, which was unveiled at a special event on September 7, 2016.  - Topple is a game developed and published by ngmoco for the iOS platform . It is available for download on the iPhone and iPod touch on the App Store or iTunes . A sequel entitled Topple 2 was released on March 8 , 2009 .  - The iPod is a line of portable media players and multi-purpose pocket computers designed and marketed by Apple Inc. The first version was released on October 23, 2001, about 8 months after iTunes (Macintosh version) was released. The most recent iPod redesigns were announced on July 15, 2015. There are three current versions of the iPod: the ultra-compact iPod Shuffle, the compact iPod Nano and the touchscreen iPod Touch.  - The iPod Touch (stylized and marketed as iPod touch) is an iOS-based all-purpose handheld PC designed and marketed by Apple Inc. with a user interface that is touchscreen-based. It can be used as a music and video player, digital camera, handheld game device, and personal digital assistant (PDA). It connects to the Internet only through Wi-Fi base stations, does not use cellular network data, and is therefore not a smartphone, though it has a similar design to the iPhone and is often referred to as the "iPhone without a phone". Furthermore, it does not fit in Apple's iPhone accessories such as their leather cases. As of May 2013, 100 million iPod Touch units had been sold. It is also the most popular iPod model.  - iTunes (or ) is a media player, media library, online radio broadcaster, and mobile device management application developed by Apple Inc. It is used to play, download, and organize digital downloads of music and video (as well as other types of media available on the iTunes Store) on personal computers running the macOS and Microsoft Windows operating systems. The iTunes Store is also available on the iPhone, iPad, and iPod Touch.    After reading the paragraphs above, choose the best answer for the entity that related to 'topple' with the relationship of 'input device'.  Choices: - keyboard  - touchscreen
The answer is:
touchscreen