※ 주어진 부분에 들어갈 가장 적절한 것을 고르시오. [문 14～문 15] A growing number of people are seeking medical attention for vitamin D deficiency, a common condition among those who spend a lot of time indoors. It is well known that vitamin D deficiency can affect one's muscles, bones and immunity and is even associated with cancer. Vitamin D is produced by the body in response to skin being exposed to sunlight. A lot of women, however, wear sunscreen before they go out, and this often makes it more difficult for their body to produce vitamin D― as ___________________________.