In Addition to Stalin's Growing Paranoia, What Prompted the Great

In addition to Stalin's growing paranoia, what prompted the Great Terror?

A) the growing threat of Nazi military activities
B) an attempted coup by top military generals
C) the closing of the Gulag and the resurrection of the Left Opposition
D) a failure to fully achieve goals set by the first Five-Year Plan
E) widespread strikes and civil unrest protesting Stalin's totalitarian rule