單項選擇題

A refrigeration system contaminated with moisture can be affected by （）.

A.acid formation
B.sludge formation
C.ice in the expansion valve
D.All of the above

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單項選擇題

R-12 is generally considered to be a safe, nontoxic, nonflammable, and non-explosive refrigerantIt can, however, become highly toxic when （）.

A.superheated outside the system
B.in contact with an open flame
C.heated to the boiling point
D.All of the above

單項選擇題

Which of the following statements is/are true regarding hydraulic pumps in general? （）

A.Variable volumes can be obtained with gear pumps only by variation of the pump drive speed
B.A radial piston pump houses sliding pistons in a stationary cylinder block through which passes a rotating pintle or ported shaft
C.The amount of fluid displaced per revolution of an axial piston rotary pump is dependent on the angle formed between the cylinder block and valve plate
D.All of the above