Which answer corresponds with a low compression scenario showing changes in emissions?

In a low compression scenario, it's essential to understand how engine performance and emissions are affected. When compression is low, the combustion process can be incomplete, leading to higher levels of unburned hydrocarbons (HC) in the exhaust. This happens because the mixture of fuel and air may not ignite completely or the combustion process may not reach the optimal temperature and pressure needed for full combustion.

An increase in hydrocarbons is a common indication of incomplete combustion, which can occur due to various factors associated with low compression, such as worn piston rings, damaged cylinder walls, or leaking valves. These issues prevent the engine from achieving efficient combustion, resulting in more HC being emitted into the atmosphere.

Other emission components may not show notable changes in this scenario. For example, CO emissions might remain stable if the air-fuel ratio remains similar even if combustion efficiency is reduced. CO2 levels may decrease because less fuel is being burned effectively, directly correlating with a potential reduction in the combustion process. Lastly, O2 levels might increase, reflecting unburned oxygen due to an incomplete combustion process, but that does not directly relate to the primary impact of increased HC emissions from low compression.

Thus, the correct answer relates directly to the expected behavior of hydrocarbon emissions when