The author implies that ______.
A. it is sometimes easier to detect supernovas by observation of the X-ray spectrum than by observation of visible wavelengths of light
B. life on the earth is endangered by its constant exposure to radiation forces that are released by a supernova
C. recently discovered meteorites indicate that the earth and other planets of our solar system survived the explosion of a supernova several billion years ago
D. lighter elements are formed from heavier elements during a supernova as the heavier elements are torn apart
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The author argues that the antigen-antibody explanation of immunity "had to be seriously qualified" because______.
A. antibodies were found to activate unstable components in the blood
B. antigens are not exactly complementary to antibodies
C. lymphocytes have the ability to bind to the surface of antigens
D. antibodies are synthesized from protein whereas antigens are made from nucleic acid
Which of the following methods does the author employ to develop the first paragraph？
Analogy.
B. Deduction.
C. Generalization.
D. Example.
According to the passage, we can expect a supernova to occur in our galaxy ______.
A. about twice each year
B. hundreds of times each century
C. about once every fifty years
D. about once every other century
According to the passage a neutron star is ______.
A. a gaseous cloud containing heavy elements
B. an intermediate stage between an ordinary star and a supernova
C. the residue that is left by a supernova
D. the core of an ordinary star that houses the thermonuclear reactions
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