classification allows us to focus on one or two features and see something in terms of those characteristics alone. to classify plants and animals, we have to ignore all the variations that distinguish one plant from another and one animal from another. we have to focus only on those aspects that are shared by all plants and that differentiate them from all animals. we ignore the great variation that exists within each group and reduce its members to the common ground that ties all the members of that group together. as a result, we come to see objects in terms of their membership in a particular group, and we miss seeing that each is more than its group membership. trapped by the category of doors, we become blind to the three-by-seven-foot pieces of wood that are right in front of us.

이번에 고2모의고사 예비시행 b형 40번에 있던 문제입니다.
각각 밑줄친 단어 them과 its가 가리키는 것이 무엇인지 설명 좀 부탁드립니다.
친절한 답변 꼭 부탁드립니다. ㅜㅠ