Automobile Power Plants — Most Common Type Among practical automotive power plants, which is the most widely used for passenger and commercial vehicles?

Introduction / Context:
Automotive propulsion has explored many concepts, but the overwhelming majority of road vehicles worldwide have historically used internal-combustion (I.C.) engines. This question checks basic awareness of mainstream power plants.

Given Data / Assumptions:

• Conventional passenger cars, trucks, buses across the last decades.
• I.C. engines include petrol and diesel reciprocating engines.
• Not considering niche prototypes or very recent market shifts.

Concept / Approach:
Reciprocating I.C. engines balance cost, energy density, refueling speed, and mature supply chains. While hybrids and BEVs are growing rapidly, the global fleet remains dominated by I.C. engines, especially in commercial and developing markets. Gas turbines and steam engines are rare in automobiles due to efficiency, cost, and drivability challenges.

Step-by-Step Solution:
Survey practical usage: petrol and diesel engines power most vehicles.Compare alternatives: gas turbines saw limited trials; batteries alone are increasingly common but still not the historical majority.Select the option representing mainstream reality: I.C. engine.

Verification / Alternative check:
Registration and production data over many years show I.C. engines as the dominant power plant globally.

Why Other Options Are Wrong:
Gas turbine: poor part-load efficiency and cost barriers.Battery (pure BEV): growing but not historically the most common across all regions and classes.None of these: incorrect given widespread I.C. use.Steam engine: obsolete in modern autos.

Common Pitfalls:
Conflating recent EV adoption trends with long-term dominance; the question asks “most commonly used”.

Final Answer:
I.C. engine