15.What did the Danes and Geats believe as they sat by the lake?
A. Grendel was still alive.
B. Beowulf had been killed.
C. Grendel's mother would attack again.
D. The water would turn to blood.

the central idea of the above passage is following;

central idea: cultural study is very important specially archaeology. grimm's stories very well cater to the importance of cultural relevance.

explanation:

boccaccio employs the voice of his narrator dioneo to represent his ideas on the tension between masculinity and femininity.  while dioneo excites the members of the brigata and recognizes women for their unique skills and independent ideas, he concludes the decameron with a story reminiscent of the society from which these young aristocrats escaped, revealing misogynistic overtones.  dioneo boccaccio is able to explore the gender disparity which is inherent in 14th century florentine society.