The correct answer is: C. both (a) and (b)
Uttarakhand has international boundaries with China in the north and north-east, and with Nepal in the east.
The northern border of Uttarakhand is the Line of Actual Control (LAC) with China. The LAC is a disputed border that runs through the Himalayas. The LAC is not formally demarcated, and there have been several incidents of conflict between India and China along the LAC.
The north-eastern border of Uttarakhand is also the LAC with China. The LAC in this area runs through the Himalayas and the Tibetan Plateau. The LAC is not formally demarcated, and there have been several incidents of conflict between India and China along the LAC.
The eastern border of Uttarakhand is with Nepal. The border between Uttarakhand and Nepal is a long, mountainous border that runs through the Himalayas. The border is formally demarcated, and there have been no major incidents of conflict between India and Nepal along the border.