What was the origin of Apollonius Dyscolus' nickname 'ho dúskolos', meaning 'the difficult' or 'crabby/grouchy'?

A. His habit of using complex grammatical structures in his writing
B. His reputation for being a fierce competitor in debates with other grammarians
C. His tendency to be extremely frugal and thrifty in his daily life
D. All of the above, including his sour temper due to living in poverty
Answer: 