I would say D as it shows a sense of in-security and a logical appeal.
I'd say A.
The word "describing" or almost anything ending with "ing" signifies an action occuring now, or in the present. B, C, and D use "when describing" which leads to the assumption that these things listed are taken into account while the landscape is being described but answer choice A uses "when they describe" which is passive rather than active.
Sentences that delay the main point until the end are called periodic. Hope this helps
