Mark the letter A, B, C, or D on your answer sheet to indicate the best arrangement of utterances or sentences to make a meaningful exchange or text in each of the following questions from 13 to 17.

a. In places like Beijing, China, the air is often full of smoke and harmful gases from cars and factories.
b. Children and elderly people are especially affected by the dirty air and can get sick more easily.
c. The pollution makes it hard to breathe, and people sometimes wear masks to protect themselves.
d. In many big cities, air pollution is a serious problem.
e. To improve the situation, the government is working on better public transportation and encouraging the use of clean energy.