History's First Critical Chain Reaction Took Place in an Atomic

Multiple Choice

History's first critical chain reaction took place in an atomic pile. The neutrons from fission reactions caused other fission reactions to occur. What would be the most effective method to stop the fission reaction from proceeding?

A) throw water on the pile to cool the reaction
B) add more neutrons to the reaction
C) place strong neutron absorbers into the pile
D) none of the choices