Which best explains why readers sometimes need to make inferences?
a. authors want their writing to be difficult for the reader to understand.
b. authors do not want their readers to use prior knowledge when reading.
c. authors sometimes hint at certain ideas rather than state them directly.
d. authors often forget to include important details about a situation.

explanation: the line "to save the day, harry must get past a scary three-headed guard dog" from the summary best justifies the conclusion that harry potter and the sorcerer’s stone was influenced by ancient greek mythological literature. the three other choices had nothing to do with ancient greek literature - and the words "three-headed guard dog" are what makes that choice the correct answer.