| <!--[if !supportLists]-->1.
<!--[endif]-->Humans have been damaging the
environment for centuries by overcutting trees and farming too intensively, and
though some protective measures, like the establishment of national forests
and wildlife sanctuaries, having been taken decades ago, great increases in
population and in the intensity of industrialization are causing a
worldwide ecological crisis.
(A) though some
protective measures, like the establishment of national forests and wildlife sanctuaries,
having been taken decades ago, great increases in population
(B) though some
protective measures, such as the establishment of national forests and wildlife
sanctuaries, were taken decades ago, great increases in population
(C) though some
protective measures, such as establishing national forests and wildlife
sanctuaries, having been taken decades ago, great population increases
(D) with some
protective measures, like establishing national forests and wildlife
sanctuaries that were taken decades ago, great increases in population（B）
(E) with some
protective measures, such as the establishment of national forests and wildlife
sanctuaries, having been taken decades ago, great population increases
Not very difficult to get th e right answer. But what's the structure of this sentence. | 
