The correct answer is: c) Only helicopter services.
Arunachal Pradesh is a landlocked state in north-eastern India. It is the largest state in the country by area, but it has the lowest population density. The state is hilly and mountainous, with a large number of rivers and streams. The terrain makes it difficult to build roads and railways, so air travel is the most common way to get around.
There are a few small airports in Arunachal Pradesh, but they are only used for domestic flights. The state is also served by a number of helicopter services, which provide a more reliable and efficient way to travel.
The other options are incorrect because they do not accurately reflect the state of air connectivity in Arunachal Pradesh. Option a) is incorrect because there are only a few small airports in the state. Option b) is incorrect because there are a number of helicopter services that operate in the state. Option d) is incorrect because there is some air connectivity in the state, although it is limited.