I might be wrong, but I think the error is the way they spelled okay. When you are writing in an essay or any other forms of writing, I think you’re supposed to spell the word out instead of abbreviating it.
I hope this helps :)
Answer:
I think it's b but I'm not sure sorrt
D. Cloister, the meaning is cloister<span> (from Latin claustrum, "enclosure") is a covered walk, open gallery, or open arcade running along the walls of buildings and forming a quadrangle or garth.</span>
I believe your best answer would be terrace
C. It puts emphasis on the paragraph's main proposal and call to action.