What advantage over an aquatic organism does a terrestrial organism have with the regard to obtaining oxygen for the respiration? 

Concept: Air contains around 21% oxygen whereas water has 1% oxygen in broken down state. A earthbound living being is able to urge a few more times oxygen than a sea-going creature. 

Usually, the reason that the earthly life form has the advantage of getting more oxygen that oceanic life forms. Therefore, the advantage over an aquatic organism the terrestrial organism has with regard to obtaining oxygen for the respiration is that the air contains about 21% of oxygen while water has 1% oxygen in dissolved state and the terrestrial organism is able to get several more times oxygen than an aquatic animal.

Hence, the correct answer is option C.