Piston rings — classification Automotive pistons typically employ two categories of rings. Identify the correct pair.

Introduction / Context:
Piston rings provide gas sealing and oil regulation. Most engines use a combination of upper compression rings and lower oil-control assemblies for reliable operation.

Given Data / Assumptions:

• Typical ring pack: two compression rings and one oil-control ring (three-piece).
• Cylinder made of cast iron or liners in aluminum blocks.
• Normal lubrication and honing crosshatch present.

Concept / Approach:
Compression rings seal combustion gases and transfer heat from the piston to the cylinder wall. The oil-control ring meters oil film, scraping excess and returning it through drain holes to the crankcase.

Step-by-Step Solution:
Top rings: provide primary gas seal and heat path.Oil ring: controls oil, often with expander and side rails.Thus, the two classes are compression rings and oil-control rings.

Verification / Alternative check:
Service literature labels rings as compression (top/second) and oil-control; other names are colloquial.

Why Other Options Are Wrong:
“Sliding seal,” “pressure,” “sealing,” or “relief” rings are nonstandard terms.

“Oil scrapper” is an informal synonym but paired with oil-control duplicates function while omitting compression rings.

Common Pitfalls:
Improper ring end gaps, wrong orientation, or carboned drain holes cause oil burning and poor sealing.

Final Answer:
compression and oil-control rings