Tsar Nicholas II and Tsarina Alexandra were the Romanov rulers of Russia when the Bolshevik revolution took place in 1917. During this revolution, Tsar Nicholas II was overthrown, and the majority of his family members were killed. The remains of two of the Tsar and Tsarina’s children, Alexei and Anastasia, were never found. Suppose two people came forward who claim to be the missing Romanovs. Which technology could only be used to identify Alexei?