Chekhov is considered the
a. first russian playwright
b. master of suspense and horror
c. father of the modern short story
d. father of detective fiction

I would say that Chekov is considered the father of the modern short story but he also wrote plays and is also considered a key figure in the introduction of modernism into the theater along with Ibsen and Strindberg. He made some innovations in his short stories. 

The gregorian chant was a major cultural milestone in the middle ages. it was one of the first codified forms of music meant to be played as written, where previously it was difficult to mass-produce and disseminate any music. what's more, these chants were also some of the first examples of musical notation: the notes and bars of today's music sheets are a reflection of centuries of evolution beginning with these chants. it became official throughout the entirety of the catholic church, meaning that nearly all of europe followed this musical notation and styling.