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單項選擇題

It is usual to identify the fluids in pipes by bands of paint at intervals, and the engineer should familiarize himself with the code in use.According to the above sentence, which of the following statements is true?()

A.People can know the types of fluids in pipes by feeling with hands
B.There are series of rings painted in the pipes to show various fluids
C.Engineers should wear cards standing for ranks
D.Engineer knows his own code very well

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