The correct answer is: a) Siang.
The Siang River is the largest tributary of the Brahmaputra River. It flows through the Indian state of Arunachal Pradesh and the Chinese province of Tibet. The Siang is a popular destination for white-water rafting and kayaking. The river is known for its rapids, which range from Class II to Class V.
The Kameng River is another popular destination for white-water rafting in Arunachal Pradesh. The river flows through the eastern part of the state and is known for its Class III and IV rapids.
The Subansiri River is a major tributary of the Brahmaputra River. It flows through the eastern part of Arunachal Pradesh and is known for its Class II and III rapids.
The Lohit River is a major tributary of the Brahmaputra River. It flows through the northeastern part of Arunachal Pradesh and is known for its Class III and IV rapids.
In conclusion, the Siang River is the best river for white-water rafting in Arunachal Pradesh. It is known for its rapids, which range from Class II to Class V.