Answer:
The letter is an important part of the story “the letter”. It is the soul of the story. It is the nucleus around which the story develops. Towards the end of Ali's life, the letter became the purpose of his existence.
Kaplan states that
Some environments bring out the best in people, others do exactly the opposite. He and his wife believed that what people really needed in their lives was exposure to nature. In a series of studies, the couple demonstrated that an office window that overlooks a natural scene helps people relax, thus fighting off one of the primary threats to competence, mental fatigue. Both energy and job enthusiasm rose among people who had a chance to glance out the window occasionally and see something, even if it was only a single tree.
The answer is D, because there are two nouns put together, while another before it is identifying it.
