Which of the following statements are true? Answer using codes given after the statements:

(a) Scheduled tribe population is negligible in their presence in Ganga valley.

(b) Religions minorities have greater representation in the population located in the geographical periphery of India.

(c) All the tribal communities in North-East India speak one or other languages belonging to Sino-Tibetan family.

(d) Kerala has the highest concentration of scheduled castes in its population.