Final answer:
It is true that vocal fillers are undesirable words used to cover pauses in speech. They can reduce speech fluency and speaker credibility. Practicing and using single-word alternatives can improve speech clarity.
Step-by-step explanation:
The statement that unnecessary and undesirable words used to cover pauses are called vocal fillers is true. Vocal fillers such as 'um', 'ah', and 'like' can obscure your message and detract from the fluency of your speech, reducing the impact and credibility of what you're saying. While brief pauses may be used effectively for dramatic effect or to allow information to be processed, awkward pauses filled with vocal fillers suggest a lack of preparation or nervousness. Practicing speech can help reduce the use of fillers. Instead of using filler phrases, it's often better to use a single-word alternative or restructure your sentence to be more concise and direct, thus enhancing clarity and engagement.