Explanation:

The Kuka Movement was a religious and social reform movement that emerged among the Sikhs in Punjab during the mid-$19^{th}$ century. Its followers were known as Kukas, and the movement was also referred to as the Namdhari movement. The Namdharis were distinguished by their white clothes, straight turbans, and strict adherence to Sikh principles, including vegetarianism and abstinence from alcohol and drugs. - Option A (Nirankari): The Nirankari movement is another reformist Sikh sect, but its followers are not referred to as Kukas. - Option B (Namdhari): The Kuka Movement is synonymous with the Namdhari movement, and its followers are indeed called Kukas. This is the correct answer. - Option C (Tribal People from Afghanistan): This refers to a completely different group and context, unrelated to the Kuka Movement. - Option D (Fugitives in Sindh region): This also refers to a different group and context, unrelated to the Kuka Movement.