单项选择题
A.an oil seal
B.removing heat
C.a gas seal
D.cooling the piston
单项选择题 The figure that the volume of air at BDC is divided by the volume of air at TDC is termed as（）.
单项选择题 The external circumference of a pair of main bearing shells is slightly larger than that of the bore of the housing which receives themThe difference is termed （）.
单项选择题 The external circumference of a pair of main bearing shells is slightly （） that of the bore of the housing which receives themWhat’s the meaning of “that” in the sentence above?