The correct answer is: a) Khasi people.
The Pnar language is a member of the Mon-Khmer language family and is spoken by the Khasi people of Meghalaya, India. It is a tonal language with six tones. The Pnar language is written in the Roman script.
The Garo people speak the Garo language, which is a member of the Tibeto-Burman language family. The Jaintia people speak the Jaintia language, which is also a member of the Mon-Khmer language family. The Biate people speak the Biate language, which is a member of the Kuki-Chin language family.
The Pnar language is closely related to the Khasi language, and the two languages are mutually intelligible. The Pnar language is also related to the Garo language, but the two languages are not mutually intelligible. The Pnar language is not related to the Jaintia language or the Biate language.