The correct answer is: a) Permanent snow cover
The high altitude areas of Arunachal Pradesh experience permanent snow cover. This is because the high altitude areas are located in the Himalayas, which are a mountain range that is known for its cold and snowy climate. The snow in the high altitude areas of Arunachal Pradesh does not melt all year round, which is why it is called permanent snow cover.
The other options are incorrect because they do not accurately describe the climate of the high altitude areas of Arunachal Pradesh. Option b, occasional snowfall, is incorrect because the snow in the high altitude areas of Arunachal Pradesh does not melt all year round. Option c, no snowfall, is incorrect because the high altitude areas of Arunachal Pradesh do experience snowfall. Option d, frequent snowfall, is incorrect because the snow in the high altitude areas of Arunachal Pradesh does not melt all year round, which means that it does not snow frequently.