= Solution
An <alpha decay> decreases <mass number> by four and <atomic number> by two; a <beta-minus decay> keeps the <mass number> fixed and increases <atomic number> by one. Therefore
$$
\boxed{\mathrm{A}={}^{239}_{93}\mathrm{Np},\qquad\mathrm{B}={}^{239}_{94}\mathrm{Pu},\qquad\mathrm{C}={}^{235}_{92}\mathrm U.}
$$
The beta-minus step converts a neutron to a <proton> with emission of an <electron> and an <electron antineutrino>. It is not capture of an orbital <electron>, which would change the <atomic number> in the opposite direction.
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