The canterbury tales was a popular book of the period because it
a. contained many different stories.
b. had characters from all walks of life.
c. was written in easy-to-understand language.
d. described middle- and upper-class fashions

The Canterbury Tales was a popular book of the period because it c) was written in easy-to-understand language. This was because it was written in Vernacular English language, at a time where most tales were written in Latin, French or Italian. Chaucer at his time was part of the time of this trend where English-language stories were taking off.

They said that the world was flat