Mark the letter A, B, C, or D on your answer sheet to indicate the correct arrangement of the sentence to make a meaningful paragraph/letter in each of the following questions.

a. This situation not only poses serious health risks to the population but also affects the environment and quality of life in the city.
b. Recently, Hanoi has been recognized as one of the most polluted cities in the world, raising concerns among its residents and authorities.
c. Therefore, implementing stricter regulations on emissions and promoting sustainable practices is crucial for improving air quality.
d. In summary, addressing Hanoi's pollution crisis is essential for the well-being of its citizens and the preservation of the environment.
e. The high levels of air pollution are primarily attributed to rapid urbanization, vehicle emissions, and industrial activities in the area.