TOEFL Listening: TPO-TOEFL阅读TPO - O6TRKS7H0T0496Q4N$

According to paragraph 5, which of the following is a factor responsible for the greater air turbulence in urban environments? A. The high speed of the winds travelling above cities B. The greater rainfall totals recorded in cities C. Attempts to reduce urban air pollution D. The effects of tall buildings on airflow