Which of the following substances is commonly added to petroleum fuels to improve combustion?

The correct choice, which is additives, reflects the substances commonly incorporated into petroleum fuels to enhance their combustion properties. These additives are formulated to target specific aspects of fuel performance, such as improving combustion efficiency, reducing emissions, and preventing engine deposits.

Additives in fuels can include a variety of compounds, such as octane boosters, anti-knock agents, and stabilizers, which help maintain fuel quality over time. By optimizing the combustion process, these additives contribute to smoother engine operation, better fuel economy, and reduced emissions, making them essential for modern fuel formulations.

In contrast, while detergents can be considered a type of additive, the term "additives" encompasses a broader category that includes several types of chemicals aimed at improving fuel performance. Therefore, the more general term "additives" is the most accurate answer in this context. Other options, like red dye, serves specific regulatory and identification purposes but do not improve combustion directly. Solvents can impact fuel properties, but they are not primarily used to enhance combustion.