A prepositional phrase consists of the preposition and its complement. From the given sentences above, the sentence in which the prepositional phrase best modifies the verb saw is option C. Through the window, I saw the bird flying. The prepositional phrase in this sentence is "through the window".
A detail is essential in a passage if it adds to the overall idea of the passage. In this passage, the overall idea is stated in the first sentence, several key human errors contributed to the spread of the Chicago fire of 1871. That means that key details in this passage will be something related to a human error. Out of all of our choices, the first one seems the most like a human error. The second, third, and fourth choices seem more like details then like essential details. That means that the answer to the question is John Dorsey sounded a general alarm during the blaze.
