单项选择题

Implied but not stated: ________.

A．precise timekeeping is essential in science
B．scientists expect to disprove Einstein’s relativity theories
C．atomic clocks will be important in space flight
D．the rate of vibration of an atom never varies

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单项选择题

From the selection, we may assume that temperature changes ________.

A．affect only ammonia molecules
B．may affect the vibration rate of atoms
C．affect the speed at which the atoms travel
D．do not affect atoms in any way

单项选择题

An appropriate title for this selection would be ________.

A．A Peacetime Use of the Atom
B．Atoms and Molecules
C．The Satellite Timekeepers
D．The Role of the Clock