In this experiment, the famous professor showed three different ________ to the study of physics.(2012·河北保定中学月考)
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A
methods
B
ways
C
approaches
D
means
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In fact, _______ one cause that leads to the problem. 
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A
cattle is
B
cattle are
C
cattles are
D
the cattles are
He, a Nobelist, made great ______________ to researching in this area.
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A
encouragements
B
constitutions
C
breakthrough
D
contributions