What does a laser typically consist of?

A laser typically consists of a few essential components that include a gain medium, an energy source, and an optical cavity. The selection indicating "a case with two red knobs and four identical things" aligns well with common depictions and descriptions of lasers.

In many laser systems, the "two red knobs" could represent controls for tuning or adjusting the laser's output, while the "four identical things" could refer to the mirrors or other components that are often found inside the optical cavity of the laser, such as multiple laser diodes in certain configurations. Generically, the laser operates by stimulating a medium and using the optical components to amplify and direct the light produced.

This representation encapsulates the complexity of how lasers function, beyond just their external appearance. It highlights how their internal mechanisms are made up of multiple key components that work together to produce coherent light. Other options do not support the typical components and functionalities of a laser as accurately as this choice.