OG12-118求助！！

118. The World Wildlife Fund has declared that global
warming, a phenomenon most scientists agree to be
caused by human beings in burning fossil fuels, will
create havoc among migratory birds by altering the
environment 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’ burning of fossil fuels,
(D) which most scientists agree on as a phenomenon
caused by human beings who burn fossil fuels,
(E) which most scientists agree to be a
phenomenon caused by fossil fuels burned by
human beings,

我的疑问是：答案c选项的所有格+-ing形式不简洁啊。如OG12-24题所说：

the -ing form of a verb can be used as a noun
(e.g., running is her favorite sport), but it is often
awkward, particularly when used with a
possessive, as in this case.

请NN帮我解释一下。谢谢啦~