Which of the following castes is not included in the prehistoric castes of Himalayan region?

The correct answer is (a) Gandhary.

The prehistoric castes of the Himalayan region are:

• Yaksha: A race of nature spirits or demigods in Hindu mythology. They are often depicted as being half-human and half-animal, and they are said to live in the forests and mountains.
• Kinnar: A race of people who are said to be half-human and half-bird. They are often depicted as being beautiful and graceful, and they are said to live in the mountains and forests.
• Shak: A race of people who are said to be half-human and half-snake. They are often depicted as being powerful and wise, and they are said to live in the mountains and forests.

Gandhary is not a prehistoric caste of the Himalayan region. It is a caste of people who are said to be descended from the Gandharvas, a race of musicians and dancers in Hindu mythology. The Gandharvas are said to live in the heavens, and they are often depicted as being beautiful and handsome.