The correct answer is $\boxed{\text{A. 2 alpha 1 beta}}$.
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms into an atom with a mass number that is reduced by four and an atomic number that is reduced by two. Beta decay is a type of radioactive decay in which a beta particle (electron or positron) is emitted from an atomic nucleus, transforming the atomic nucleus into an atom with the same mass number but a different atomic number.
In three consecutive disintegrations, the radioactive element will emit two alpha particles and one beta particle. The first alpha particle will reduce the mass number of the element by four and the atomic number by two. The second alpha particle will reduce the mass number of the element by four and the atomic number by two again. The beta particle will not change the mass number of the element, but it will increase the atomic number by one. Therefore, the final product of the three consecutive disintegrations will have a mass number that is four less than the original element and an atomic number that is one greater than the original element.
Option B is incorrect because it only emits one alpha particle and one beta particle. Option C is incorrect because it emits two beta particles and one alpha particle. Option D is incorrect because it emits two beta particles and two alpha particles.