Which one of the following equations is correct for the heterogeneous thermal reactor?
(a) Rate of neutron production = Rate of neutron leakage - Rate of neutron absorption
(b) Rate of neutron production = Rate of neutron absorption - Rate of neutron leakage
(c) Rate of neutron production = Rate of neutron leakage + Rate of neutron absorption
(d) Rate of neutron production = Rate of neutron absorption + Rate of neutron leakage