Option A is the correct answer for the above question.
Explanation:
The keyboard is a device, by which a human can instruct the computer in the text form. There are so many keyboards in which, thumb keyboard is one of them. The thumb keyboard is found in mobile phones, smartphones or PDA phones, which is used for personal use. It is a designed layout of the keyboard that can be placed on the hand of the human and a person can type on its with the help of his thumb.
The above question asked about the type of the keyboard which is used in various smartphones and other phones. That keyboard is thumb keyboard which is described above and it is stated from the option A. So option A is the correct answer while the other is not because--
Option B states about the traditional keyboard which is used for the PC only.
Option C states about the Notebook keyboard which is used for the Notebook computers only.
Option D states about combination which is not a type of keyboard.
