The Scorpius-Centaurus OB Association Is Predicted to Have Produced a Supernova

The Scorpius-Centaurus OB association is predicted to have produced a supernova about 2 million years ago.What led to this prediction?

A) A supernova remnant with the appropriate location and age was found.
B) O and B stars are massive stars, many of them over 25 solar masses, and they would supernova.
C) In a close association, collisions between stars are expected, and collisions would raise the mass to the supernova range.
D) Shock waves from the direction of Scorpius-Centaurus still pass by Earth at frequent intervals.