The correct answer is A. the development of paper money and gun powder.
During the Song Dynasty (960-1279 AD), significant advancements were made, including the introduction of paper money as a means of promoting trade and the invention of gunpowder, which would later change warfare.
The other options, such as the development of moveable type (which was developed later), microscopes, telescopes, and certain other inventions mentioned, were not attributed to the Song Dynasty specifically.