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單項(xiàng)選擇題

Additives （） protective layers on metal surfaces guarding them against corrosion.

A.damage
B.form
C.dissolve
D.contaminate

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單項(xiàng)選擇題

Acid solution（） in the system can be tested from time to time by putting some on to a piece of lime.

A.strength
B.dense
C.percentage
D.velocity

單項(xiàng)選擇題

According to the way the energy of the exhaust gases is utilized, pressure-charging can be divided into two main systems, namely, the constant-pressure system and （）.

A.the pulse-phase system
B.the pulse Doppler system
C.the pulse system
D.the pulse interval

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