Agoraphobia. Agoraphobia is an irrational and intense fear which a person experiences when she is on some place where she feels that escape would be difficult or impossible (for example: a lot of people on one place, wide streets, train or bus trips, cinema, theaters...).
The answer would be letter D. Insulated heated pipes, gravel pads, and wood piles are being used to build on top of the permafrost. Permafrost is a ground that being frozen at or below zero of water in two years or more.
