Sleeping pills had been showing up with regularity as a factor in traffic arrests, sometimes involving drivers who later claim that they have no memory of getting behind the wheel after ingesting the pills.
A) Sleeping pills had been showing up with regularity as a factor in traffic arrests
B) Sleeping pills had been showing up with regularity as factors in traffic arrests
C) Sleeping pills have been showing up with regularity as a factor in traffic arrests
D) Sleeping pills have been showing up with regularity as factors in traffic arrests
E) Sleeping pills have been showing up with regularity in traffic arrests

The OA is C
I am a little confused. What is the correct option? I though the option A was right.