Which of the following statements regarding Gosu standards is true?

The statement that constants should be assigned a name using all capital letters with underscores is correct because it follows the widely accepted conventions in programming for defining constants. Constants are typically declared in this way to clearly distinguish them from regular variables, indicating that their values are not intended to change throughout the execution of the program. Using uppercase letters makes them easily recognizable, and underscores help in separating words, which enhances readability.

In contrast, the other statements do not align with established standards for Gosu or general programming practices. For example, using camel case for constants can lead to confusion with variable naming conventions, which usually follow camel case. The notion that all classes must implement interfaces is not a requirement in Gosu, allowing flexibility in design. Lastly, while it's generally a good practice to avoid special characters in variable names for clarity, not all languages impose a strict rule against them, and Gosu does permit certain characters in variable names.