Explanation:

- The statement means everyone can testify in court unless they cannot understand questions or give rational answers.

- Reasons for incompetence include: being too young (tender years), very old, having a disease (physical or mental), or any similar cause.

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- Option 1: Child witness

- Refers to very young persons who may not understand court questions due to age.

- Option 2: Adult witness

- Adults are generally presumed competent unless affected by illness or disability.

- Option 3: Dumb witness

- "Dumb" means mute; such witnesses may testify using alternative ways (writing/signs) if they understand and can answer.

- Option 4: Lunatic witness

- Someone with mental disorder; considered competent if able to understand and answer rationally at the time.

Correct Answer: Child witness (Option 1) — the statement specifically relates to competence issues due to tender years.