\noindent\textbf{43.} The length of a steel suspension bridge was 900 meters in the coldest year and reached 900.9 meters in the hottest year of that year. The difference between the highest and lowest temperatures of the bridge in that year is how many degrees Celsius?
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\noindent ($\alpha = 1.25 \times 10^{-5}\,\mathrm{K}^{-1}$)
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\noindent (1) 70 \hfill (2) 80 \hfill (3) 90 \hfill (4) 100
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