A. Monthly B. Quarterly C. Once a year D. The answer depends on usage: D. Depending on usage

A. Cylinder head and air liner B. Piston and piston rod C. Valve assemblies and lubrication systems D. These are all answers: D. all of the above are

A. Wear of cylinder head and air liner B. Piston and piston rod damage C. Valve assembly failure D. These are all answers: D. all of the above are

A. Price and brand B. Performance, price and brand C. Viscosity and quality of lubricating oil D. Production date and transportation method Answer: C. Viscosity and quality of lubricating oil

A. Inspect reinforced gas piping B. Replace the leaking valve C. Check or replace air valve D. These are all answers: D. all of the above are

A. Stable growth B. Volatility growth C. Declining year by year D. Stagnation Answer: A. steady growth

A. Price and brand B. Performance, price and brand C. Service quality and reputation D. Production date and transportation method Answer: C. Service quality and credibility

A. Price and brand B. Performance, price and brand C. Market share and technological innovation D. Production date and transportation method Answer: C. Market share and technological innovation

A. Price and brand B. Performance, price and brand C. Market demand and technological development D. Production date and transportation method Answer: C. Market demand and technological development

A. Increase noise B. Reduce efficiency C. Intelligent and energy-saving D. Reduce maintenance Answer: C. Intelligent and energy-saving