单项选择题

(The age of) a geological sample can (be estimated) from the ratio of radioactive to nonradioactive carbon (present) in the object (is examined).

A．The age of
B．be estimated
C．present
D．is examined
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单项选择题
Years after the accident he was still ______ by images of death and destruction.
A．twisted
B．haunted
C．dipped
D．submerged
单项选择题
No form of government in the world is ______ ; each system reflects the history and present needs of the region or the nation.
A．influential
B．dominant
C．integral
D．drastic
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