33.下列有關自動背壓式濾器（Automatic backwash strainer）的敘述，何者正確？ (A)其網目必須是在50目（Mesh）以下 (B)其在進出口的壓力差達到某設定值時，即自動沖洗 (C)當需要清洗濾器時，其系統必須暫停流通 (D)其可引進空氣作為沖洗介質，以提升效果

10.Longitudinal vibration of propulsion shafting systems is often excited by the variable thrust developed by the propeller due to the non-uniform wake pattern in which it operates. The predominant periodic component of the thrust developed by a propeller occurs at blade-rate frequency, i.e., the number of propeller blades times the rotational frequency of the shaft. For a four-blade propeller running at 60 rev/min, what is the predominant periodic frequency that excites the longitudinal vibration of the propulsion shafting systems? (A)1 Hz (B)2 Hz (C)3 Hz (D)4 Hz

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