다음 글의 밑줄 친 부분 중, 어법 상 틀린 것은?
a forest is full of many different kinds of trees ─ they are all sizes and shapes and shades of color. it is hard to imagine a pine tree wishing it ① were an oak. instead, each tree catches raindrops and reflects the sunshine in its own way. we often find ourselves ② envying others. we think they have more money or more friends. we see them as better looking or luckier in some way than we are. it is ③ so easy to overlook our own gifts when we do this. we get fooled by what looks good and forget that all human beings have some weaknesses and pain, just as we ④ are. like the trees in the forest, we each have our own unique beauty and talents. if we believe in ⑤ ourselves, rather than envy those around us, we will grow green and tall in our own way.

중 they are all sizes and shapes and shades of color. it is hard to imagine a pine tree wishing it ① were an oak.이 외 맞는 구문인지 설명 좀 ㅠㅠㅠㅠ