题目内容

_____earth scientists understand how and why earthquakes happen, forecasts are usually inaccurate.
[     ]
A. As
B. While
C. Because
D. If
B
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[     ]
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[     ]

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[     ]

A. Since
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[    ]
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[     ]
A. if          
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[     ]
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[     ]
A. because; why                  
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[     ]
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