【名词&注释】
脑出血(cerebral hemorrhage)、热应力(thermal stress)、往复泵(reciprocating pump)、安全阀(safety valve)、文化程度(education level)、行政主管部门(executive branch)、原动机(prime mover)、交管部门
[单选题]If clearance between a piston and the cylinder wall is excessive, piston slap will occur. The slap itself is caused by_____.
A. alternation of side thrust
B. a breakdown of the lube oil film on the cylinder
C. worn piston boss piston pin bearings
D. fluctuating gas pressure in tile combustion space