Final answer:
The Sumerian belief system describes the afterlife as gloomy, reflecting their view of the underworld as a dark and joyless place.
Step-by-step explanation:
According to the Sumerian belief system, the adjective that best describes the afterlife is gloomy. The Sumerians had a very somber and fatalistic view of the afterlife, which was reflected in their myths and religious texts. Their underworld, known as Kur, was portrayed as a dark, dusty, and dreary place where souls existed in a state of shadowy existence, devoid of the pleasures and comforts of life. Terms like fearful, heavy-hearted, and horrified are associated with negative emotions that can relate to descriptions of the afterlife, but in the context of the Sumerian belief system, gloomy is the most fitting description. The other options, such as happy, exciting, or scary, do not as accurately capture the spirit of the Sumerian afterlife as the option gloomy does.