[单选题]

E．ach cylinder liner on the marine medium speed engines _____.
A．is usually cooled by sea water
B．can be replaced when worn out
C．is in direct contact with the water in the bore of the cylinder
D．can t expand when heated

E．ach cylinder liner on the marine medium speed engines _____.A．is usually cooled by sea waterB．can be replaced when worn outC．is in direct contact with the water in the bore of the cylinderD．can t expand when heated