单项选择题
A.boiling and cavitations; low temperature
B.boiling and cavitations; pressurized
C.leaking and boiling; low temperature
D.leaking and boiling; pressurized
单项选择题 In order to improve the working conditions of the crosshead bearings, the bearing pressure is made and the peripheral speed is made in later designs（）
单项选择题 In order to control thermal stresses, some types of modern engines use pistons with（）
单项选择题 In order to keep the oil film on the cylinder liner during the running-in period, the piston rings are slightly rounded（）