Answer:
Letter D is the correct answer.
Step-by-step explanation:
In this excerpt, Valery's point is that Leonardo could not have foreseen modern air warfare, in spite of all his inventions and innovations. This can be understood when the speaker mentions "We know that, mounted on his great swan (ilgrandeuccellosopra del dosso del suomagniocecero) he has other tasks in our day than fetching snow from the mountain peaks...", which can make the reader understand that Leonardo's could not have seen farther away than his own time.