Sentence Correction

Australian embryologists have found evidence that suggests that the elephant is descended from an aquatic animal, and its trunk originally evolved as a kind of snorkel.
A. that suggests that the elephant is descended from an aquatic animal, and its trunk originally evolved
B. that has suggested the elephant descended from an aquatic animal, its trunk originally evolving
C. suggesting that the elephant had descended from an aquatic animal with its trunk originally evolving
D. to suggest that the elephant has descended from an aquatic animal and its trunk originally evolved
E. to suggest that the elephant is descended from an aquatic animal and that its trunk originally evolved



The world wildlife fund has declared that global warming, a phenomenon most scientsts agree to be caused by human begings in burning fossil fuels, will create havoc among migratory birds by altering the enviroment in ways harmful to their habitats.

a) A phenomenon most scientists agree to be caused by human beings in burning fossil fuels,
b) a phenomenon most scientists agree that is caused by fossil fuels burned by human beings,
c) a phenomenon that most scientists agree is caused by human beings's burning of fossil fuels
d) which most scientists agree on as phenomenon caused by human beings who burn fossil fuels,
e) which most scientsts agree to be a phenomenon caused by fossil fuels burned by human beings





The answers are E and C, respectively. Apart from the answer choices, however, why is it economical to say 'human being's burning' in the second question, when it is awkward to say 'organism's trying to metabolize' in the first one? Both -ing forms were used with a possessive and i'm not surr what distinguishes them. Thanks