Help!can someone help me to check if everything is right

Ais a group of letters having a special meaning that appears at the beginning of a word.

Which detail from "to build a fire" best supports the idea that most of the real yukon prospectors had little experience for surviving in cold weather? it happened. it was his own fault or, rather, his mistake. he should not have built the fire under the spruce tree. there was the fire, snapping and crackling and promising life with every dancing flame. he would have to build a fire and dry out his footgear. this was imperative at that low temperature—he knew that much. the flame he got by touching a match to a small shred of birch bark that he took from his pocket.

Based on context, the word “insoluble”most likely means?