单项选择题

A．The first group.
B．The second group.
C．The last group.
D．All the three groups.
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填空题
______ theory is used frequently to interpret light.
单项选择题
A．Artificial hearts.B．Telescopes.C．Microscopes.D．Radio telescopes.
A．Artificial hearts.
B．Telescopes.
C．Microscopes.
D．Radio telescopes.
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