The correct answer is D.

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Explanation:

Remember that the atomic number of an element tells us the number of protons in the nucleus. In alpha decay, an element loses two protons and two neutrons. In positron decay, a proton is converted into a neutron. Gamma decay, meanwhile, has no impact on the atomic number . Therefore, two alpha decays and two positron decays will yield a daughter nuclide with 6 fewer protons than the parent.