And then some bright spark calls me out of the blue, asking if I’m interested in buying a pension. What does a “bright spark” mean?

And then some bright spark calls me out of the blue, asking if I’m interested in buying a pension. What does a “bright spark” mean?
A.A brilliant idea.　　　　
B.An unexpected visitor.
C.An unpleasant memory.
D.Somebody who thinks himself smart.　
正确答案：Somebody who thinks himself smart.