Given a scientific passage and an answer, generate a question for the given answer.

Q: Passage: The global pattern of precipitation is influenced by movements of air masses. For example, there is a global belt of dry air masses and low precipitation at about 30 N and 30 S latitude. Answer: air masses

A: The global pattern of precipitation is influenced by movements of what?
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Q: Passage: Plate tectonic processes explain why we see many types of geological activity where we do. Stresses build up in some locations. These stresses may cause folding or faulting. Earthquakes strike along all three types of plate boundaries. The most damaging earthquakes are shallow focus. People in earthquake-prone regions must be aware of the potential damage from earthquakes. Seismologists have scales for measuring earthquake intensity and magnitude. Cities in earthquake zones must build safe structures. They also have guidelines for being safe in earthquakes. Earthquakes are often associated with volcanoes. Volcanoes erupt at all types of plate boundaries except transform. Volcanic eruptions can be quiet or explosive. Volcanoes have a variety of shapes. The shapes range from large shields, to classic peaks, to small cones. Supervolcano eruptions are rare but extremely deadly. Volcanic activity creates unique landforms. Hot springs and geysers result when water meets hot rock below ground. Some geological activity, both earthquakes and volcanic eruptions, is located away from plate boundaries. Answer: plate tectonics

A: What causes a lot of geological activity on the earth?
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Q: Passage: that the weak interaction could change quark flavor. It should also change neutrino flavorthat is, any type of neutrino could change spontaneously into any other, a process called neutrino oscillations. However, this can occur only if neutrinos have a mass. Why? Crudely, because if neutrinos are massless, they must travel at the speed of light and time will not pass for them, so that they cannot change without an interaction. In 1999, results began to be published containing convincing evidence that neutrino oscillations do occur. Using the Super-Kamiokande detector in Japan, the oscillations have been observed and are being verified and further explored at present at the same facility and others. Neutrino oscillations may also explain the low number of observed solar neutrinos. Detectors for observing solar neutrinos are specifically designed to detect electron neutrinos e produced in huge numbers by fusion in the Sun. A large fraction of electron neutrinos. Answer: mass

A:
A spontaneous change process called neutrino oscillations can occur only if neutrinos have what property?
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