An unknown stable nuclide after absorbing a neutron emits an electr...

An unknown stable nuclide after absorbing a neutron emits an electron, and the new nuclide splits spontaneously
P into two alpha particles. The unknown nuclide is :
(A) \( { }_{4} \mathrm{Be}^{9} \)
(B) \( { }_{3} \mathrm{Li}^{7} \)
(C) \( { }_{2} \mathrm{He}^{4} \)
(D) \( { }_{5} \mathrm{~B}^{10} \)