Which of the following best describes a conditional statement?

A conditional statement is best described as a statement that can be written in if-then form. This form directly reflects the nature of conditional logic, where a certain action (or block of code) is executed only when a specified condition is true. Essentially, if the condition evaluates to true, then the subsequent code block will run; if not, it will be skipped. This mechanism is fundamental to controlling the flow of a program and making decisions based on dynamic situations, which is why the if-then structure is so integral and widely used in programming.

Other options do not encapsulate the essence of conditional statements effectively. A statement that cannot be modified after creation, for instance, describes a constant rather than a conditional situation. A sequence of code that executes irrespective of conditions portrays regular procedural code, rather than something that hinges on specific conditions being true or false. Similarly, a statement that expresses a relationship between two variables implies a comparison or evaluation, but does not inherently involve the decision-making aspect that defines a conditional statement.