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  3. Supernovas in the Milky Way are the likeliest source for most of the cosmic rays reaching Earth. However, calculations show that

Supernovas in the Milky Way are the likeliest source for most of the cosmic rays reaching Earth. However, calculations show that

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问题 Supernovas in the Milky Way are the likeliest source for most of the cosmic rays reaching Earth. However, calculations show that supernovas cannot produce ultrahigh-energy cosmic rays(UHECRs), which have energies exceeding 1018 electron volts. It would seem sensible to seek the source of these in the universe’s most conspicuous energy factories: quasars and gamma-ray bursts billions of light-years away from Earth. But UHECRs tend to collide with photons of the cosmic microwave background—pervasive radiation that is a relic of the early universe. The odds favor a collision every 20 million light-years, each collision costing 20 percent of the cosmic ray’s energy. Consequently, no cosmic ray traveling much beyond 100 million light-years can retain the energy observed in UHECRs.
It can be inferred that the author of the passage would agree with which of the following about the origin of UHECRs that reach Earth?
选项 A、The origin is something other than supernovas in the Milky Way.
B、The origin is most likely something other than very distant quasars or gamma-ray bursts.
C、The origin is most likely no more than a little over 100 million light-years away from Earth.
答案A，B，C
解析 All three choices are correct. The question asks about claims the author would agree with.
Choice A is correct: The passage states that supernovas in the Milky Way "cannot produce ultrahigh-energy cosmic rays."
Choice B is correct: Since very distant quasars and gamma-ray bursts are "billions of light-years away from Earth," they are too far away for a UHECR to reach Earth.
Choice C is correct: The last sentence of the passage states that "no cosmic ray traveling much beyond 100 million light-years can retain the energy observed in UHECRs."
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