Problem: Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects. Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints.
What is tritium used for?
The answer is the following: production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints

Problem: According to Mahayana tradition, the Mahayana sutras were transmitted in secret, came from other Buddhas or Bodhisattvas, or were preserved in non-human worlds because human beings at the time could not understand them:
What sutras could have been preserved in non-human worlds?
The answer is the following: Mahayana

Problem: It was principally the widespread introduction of a single feature, the pointed arch, which was to bring about the change that separates Gothic from Romanesque. The technological change permitted a stylistic change which broke the tradition of massive masonry and solid walls penetrated by small openings, replacing it with a style where light appears to triumph over substance. With its use came the development of many other architectural devices, previously put to the test in scattered buildings and then called into service to meet the structural, aesthetic and ideological needs of the new style. These include the flying buttresses, pinnacles and traceried windows which typify Gothic ecclesiastical architecture. But while pointed arch is so strongly associated with the Gothic style, it was first used in Western architecture in buildings that were in other ways clearly Romanesque, notably Durham Cathedral in the north of England, Monreale Cathedral and Cathedral of Cefalu in Sicily, Autun Cathedral in France.
What is one example of a Gothic style element that was able to be incorporated because of technological innovation?
The answer is the following: the flying buttresses

Problem: Since the early history of the United States, Amerindians, AfricanAmericans, and European Americans have been classified as belonging to different races. Efforts to track mixing between groups led to a proliferation of categories, such as mulatto and octoroon. The criteria for membership in these races diverged in the late 19th century. During Reconstruction, increasing numbers of Americans began to consider anyone with "one drop" of known "Black blood" to be Black, regardless of appearance.3 By the early 20th century, this notion was made statutory in many states.4 Amerindians continue to be defined by a certain percentage of "Indian blood" (called blood quantum). To be White one had to have perceived "pure" White ancestry. The one-drop rule or hypodescent rule refers to the convention of defining a person as racially black if he or she has any known African ancestry. This rule meant that those that were mixed race but with some discernible African ancestry were defined as black. The one-drop rule is specific to not only those with African ancestry but to the United States, making it a particularly African-American experience.
When did the criteria for membership in mixed race groups diverge?
The answer is the following:
in the late 19th century