石灰石、白云石中Ca、Mg测定，C（EDTA）=0.01783mol/L标液，求其对CaO、MgO的滴定度。已知CaO的分子量为56.08、已知MgO的分子量为40.305。
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Why are removable sleeves installed on centrifugal pump shafts?（）
A. They make it easier to replace the pump shaft packing
B. They can be economically replaced as they wear out
C. They can be removed when it is necessary to lighten the weight of the pump
D. They increase the strength of the shaft
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