Concept:The high cost of lumbering in tropical rainforests is linked to the natural pattern of tree distribution.Explanation:In tropical forests, trees of the same species are widely scattered.The forest lacks pure stands where one species dominates a large area.So, loggers must move deep into the forest to find each valuable tree.They also need to build long roads and use special equipment for each extraction.This makes the operation slow, difficult, and very expensive.Answer:The main reason is the absence of pure stands of trees.Correct option: C.