单项选择题

A．20--50 years.
B．50--100 years.
C．100--120 years.
D．200--500 years.
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单项选择题
A．Blowing.B．Splitting atoms.C．Joining atoms.D．None of the abov
A．Blowing.
B．Splitting atoms.
C．Joining atoms.
D．None of the abov
单项选择题
A．mining is difficultB．it costs a lot of money to preserveC．they are difficult to be processedD．they are non-renewable
A．mining is difficult
B．it costs a lot of money to preserve
C．they are difficult to be processed
D．they are non-renewable
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