Directions: Choose the best answer.
   When Wu Kai, a Harbin resident, looked (1)_______ her apartment window on Monday, she couldn’t see anything. At first, she thought it (2)_______. Then she realized it was smog. Her husband left for work wearing a mask to (3)_______ his mouth and nose and stop him from breathing in the pollution. His regular bus wasn’t out of service (4)_______ the low visibility.
   Many people (5)________ get around. Authorities in the city closed schools and some highways on Monday. Harbin’s Taiping International Airport canceled or delayed at least 40 flights.