单选题The piston crown employs the usual jet-shaker principle with an arrangement of cooling bores in the crown so that the surface temperatures of the crown are moderate with a very even distribution（）Awater coolingBoil coolingCair coolingDcombined cooling
单选题
The piston crown employs the usual jet-shaker principle with an arrangement of cooling bores in the crown so that the surface temperatures of the crown are moderate with a very even distribution（）
A
water cooling
B
oil cooling
C
air cooling
D
combined cooling
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