Answer:The first task of a nuclear weapon design is to rapidly assemble a supercritical mass of fissile uranium or plutonium. A supercritical mass is one in which the percentage of fission-produced neutrons captured by another fissile nucleus is large enough that each fission event, on average, causes more than one additional fission event. Once the critical mass is assembled, at maximum density, a burst of neutrons is supplied to start as many chain reactions as possible. Early weapons used a modulated neutron generator codenamed "Urchin" inside the pit containing polonium-210 and beryllium separated by a thin barrier. Implosion of the pit crushed the neutron generator, mixing the two metals, thereby allowing alpha particles from the polonium to interact with beryllium to produce free neutrons. In modern weapons, the neutron generator is a high-voltage vacuum tube containing a particle accelerator which bombards a deuterium/tritium-metal hydride target with deuterium and tritium ions. The resulting small-scale fusion produces neutrons at a protected location outside the physics package, from which they penetrate the pit. This method allows better control of the timing of chain reaction initiation.
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arteries carry blood from the heart to the lungs and veins carry blood from the lungs to the heart
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Arteries carry oxygenated blood from the heart, while veins carry oxygen-depleted blood back to the heart. ... The pulmonary veins transport oxygenated blood back to the heart from the lungs, while the pulmonary arteries move deoxygenated blood from the heart to the lungs.)
C is the answer hope this helps
He set up his periodic table by the atomic mass