Which of the following best describes a block in speech?

A block in speech refers to a moment during which an individual attempts to speak but is unable to initiate or continue their speech flow. This often manifests as a pause where no sound is produced, despite the person's intention to speak. It can be a significant part of various speech disorders, including stuttering. The individual may experience tension or struggle during this moment of blockage, which contrasts with the fluidity of normal speech patterns.

The other options describe different aspects of speech or dysfluency, such as rapid sound repetition or changes in pitch, but they do not accurately define a block. Thus, the description that captures the essence of a block is one where speech initiation is interrupted, highlighting the nature of this particular speech phenomenon.