This question is based on the following passage. The sentences are numbered to help you answer the question.
(1) Do you enjoy being out in the fresh air? (2) Does nature restore your spirits? (3) You might want to consider hiking as a hobby. (4) It's a hobby you can begin with very little expense. (5) All you need to start is a good pair of hiking shoes.
The first sentence in the paragraph helps to _______ the main idea of the paragraph.
A. delay B. introduce C. explain D. specify