The correct answer is: a) Duitara.
The duitara is a traditional Khasi string instrument resembling a long-necked guitar. It is played with a plectrum and has six strings. The duitara is used in both folk and classical Khasi music.
The sarod is a long-necked, fretted string instrument from India. It is played with a plectrum and has seven strings. The sarod is used in both classical and folk Indian music.
The sitar is a long-necked, fretted string instrument from India. It is played with a plectrum and has seven strings. The sitar is used in classical Indian music.
The tambura is a long-necked, fretless string instrument from India. It is played with the fingers and has four strings. The tambura is used as an accompaniment instrument in classical Indian music.