The tip-of-the-tongue phenomenon: A. is a temporary inability to remember something you know, accompanied by a feeling that it's just out of reach. B. is clearly due to a failure in retrieval. C. reflects a permanent loss of information from LTM. D. is both a and b.

The tip-of-the-tongue phenomenon occurs when you have a temporary inability to recall a certain piece of information, but you can sense that it is just beyond the reach of your memory. It is a frustrating but common experience.

A. This option is describing the tip-of-the-tongue phenomenon accurately. It states that a person encounters a temporary inability to remember something, accompanied by the feeling that it's just out of reach. So, this option is a potential correct answer. B. This option states that the phenomenon is clearly due to a failure in retrieval. It is true that during the tip-of-the-tongue phenomenon, a person is unable to retrieve certain information, even though it is present in their memory. Thus, this option is also a potential correct answer. C. This option suggests that the tip-of-the-tongue phenomenon is a reflection of a permanent loss of information from Long Term Memory (LTM). However, the phenomenon is typically temporary, and the information can eventually be recalled. So, this option is incorrect. D. This option combines options A and B. Since both of these options accurately describe the tip-of-the-tongue phenomenon, this option is also a potential correct answer.

Since option C is incorrect and options A, B, and D are accurate descriptions of the tip-of-the-tongue phenomenon, the correct answer is: D. is both a and b.