As the size of some animals has evolved to greater sizes, the effectiveness of their adaptations that promote exchanges with the environment have also increased. for example, in many larger organisms, evolution has favored lungs and a digestive tract with
a) more branching or folds
b) increased thickness
c) larger cells
d) decreased blood supply

A) more branching or folds

Explanation:

Some animals have evolved to greater size which helped them adapt in their environment, for example, arctic mammals are larger in size because their larger size decreases the surface area to volume ratio which allow them to lose less heat as compared to smaller animals.

In many organisms, evolution has favored the lungs and digestive tract with more branching and folds. The highly branched and folded surface gives them a large surface which ensures that they get sufficient oxygen to every part of the body. It allows the absorption of more and more nutrients through the digestive tract in the body to support their huge body.

not only is it colder, it also becomes darker, less salty, and more dense.