Final answer:
The Sumerians' astronomical observations led to the discovery of the solstices and the regularity of the phases of the sun.
Step-by-step explanation:
The correct answer is b) Solstices, sun.
The astronomical observations made by the Sumerians led to the eventual discovery of the seasonal solstices and the regularity of the phases of the sun. From their study of astronomy, the Sumerians developed the "writing of heaven" and invented the calendar and its names. Sumeria's astronomical observations contributed to the discovery of the seasonal solstices and the regularity of the phases of the sun. From their observations in astronomy, the Sumerians developed a form of record-keeping known as the "writing of heaven," and they also invented the cuneiform writing system and its associated names for celestial bodies.