Was Chen Fan's plot against the eunuchs an isolated incident?
No, similar plots happened during the Eastern Han dynasty
Yes
It's unclear
It was part of a larger rebellion
Answer
No, similar plots happened during the Eastern Han dynasty. For example, in 149 AD, Cao Jie, a minister in charge of imperial household affairs, was arrested and executed on charges of conspiracy with eunuchs to seize power.
The Enigmatic Trail of Chen Fan: An Engaging English Quiz