Which of the following methods are MOST likely used to reduce the internal temperature of a computer?

Installing a protective cover usually refers to an external case or sleeve, which typically has no direct impact on internal component temperatures and might even hinder airflow if poorly designed.

Reducing display brightness affects the power consumption and heat generation of the monitor or laptop screen, but it does not significantly impact the internal temperatures of the computer's core components like the CPU or GPU.

Air circulation, achieved through fans and proper case design, is a fundamental method to draw cool air in and expel hot air from the computer case, facilitating heat dissipation from internal components.

Electronic recycling is the process of disposing of old electronic devices responsibly and has no bearing on reducing the internal temperature of a currently operating computer.

Liquid cooling, utilizing a pump, radiator, and liquid coolant, is an advanced and highly effective method for transferring heat away from high-performance components like the CPU and GPU, offering superior thermal management compared to air cooling.