单项选择题

Experiments in the photography of moving objects （） in both the united states and Europe before 1990.

A．have been conducting
B．were conducting
C．had been conducted
D．are conducted

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单项选择题
Speech is the （） ability possessed only by human beings.

A．unique
B．average
C．collective
D．single
单项选择题
（） their differences, they are united by the common desire to transform their personal commitment into public leadership.

A．But for
B．For all
C．Above all
D．Except for
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