Internal Respiration consists -
a. Cellular Respiration
b. Diffusion of Gases
c. Anaerobic Respiration
d. Both A and B

Hint: It refers to gas exchange from the respiratory membrane in the metabolizing tissues, like in skeletal muscles. Carbon dioxide and waste are also diffused to another direction, from the cells to the blood.

Complete answer:
Internal respiration is the route of diffusing oxygen from the blood, into the interstitial fluid and the cells. Oxygen is exuded from blood cells in retort to the oxygen concentration in the capillaries of blood vessels, which is regularly really low. It is also known as cellular respiration as oxygen diffuses out of the blood and carbon dioxide oozes out of the cells.

Hence, The correct answer is option (D).

Additional information:
Linked Points -
> Respiration – The method of exchanging oxygen, carbon dioxide, and many other solutes between the blood and surroundings to continue manufacturing energy through aerobic pathways.
> Breathing – A process started by muscles to pump in air or water into the lungs or over the gills.
> External Respiration – The process of exchanging solutes with the exterior environment via special tissues.
> Cellular Respiration – The process of utilizing oxygen to take out energy from organic molecules.

Note:
- A hagfish does not possess a closed respiratory system, but somewhat a system of the blood-filled sinuses with the aim of exchanging oxygen and carbon dioxide with the interstitial fluid.
- A lungfish is the only fish that has lungs, and guzzles air into the lungs, forcing it down with a gulp.
- A newt does not need to compel water over its gills, because they reside externally and exchange oxygen as the new moves.