The one that presents a main idea is number (3) "Fire, in fact, has been a significant factor in human development and progress in many ways".
The main idea of a paragraph states the primary point that the author wants to express and transmit to the reader. Generally, the main idea is announced in a single sentence and this sentence is usually located at the beginning of a paragraph. In the case of the paragraph provided, sentence 3) is the one that contains the main idea because it encompasses all the supporting details that are included in the rest of the sentences. In other words, sentences 1), 2), 4), 5), 6) and 7) provide supporting information for the main point stated in sentence 3).