Posterior one third of the tongue or base is formed by:

 # Posterior one third of the tongue or base is formed by:

A. Two lingual swelling

B. Hypobranchial eminence

C. Copula

D. Tuberculum impar

The correct answer is B. Hypobranchial eminence.

The hypobranchial eminence is a swelling in the embryonic development of the tongue that gives rise to the base of the tongue. It is located in the midline and forms the posterior part of the tongue. It develops from the third and fourth pharyngeal arches during embryonic development.

The other options mentioned are not specifically related to the formation of the posterior one third of the tongue.

A. Two lingual swellings: These refer to the anterior two-thirds of the tongue, which are formed by a pair of lingual swellings that merge during development.

C. Copula: The copula is a structure in embryonic development that contributes to the formation of the posterior part of the tongue, but it does not specifically form the base of the tongue.

D. Tuberculum impar: The tuberculum impar is a small median swelling in the embryonic development of the tongue, located at the midline in the anterior part of the tongue, and it does not contribute to the formation of the base of the tongue.

Therefore, the correct option is B. Hypobranchial eminence.