The air pollution was so bad in Harbin, in China, on October 21,2013 that the city had to close roads and schools, and cancel* hundreds of flights from its airport.
News reports said the smog (a mixture of smoke and fog) was so thick that people couldn’t see more than 10 or 20 metres in front of them.
It is also said that people could not even see the person standing next to them. The city’s website said: “You can’t see your own fingers in front of you.”
The local people said there was a “burning” smell in the air. Many people covered their noses and mouths with scarves or masks*.
The pollution was caused on several factors* including: farmers burning off old corn stalks* and crop stubble*; coal*-fired heating systems; and low winds that allowed the smoke to remain over the city.
The smog had been building up for several days. It became worse when the city turned on the public heating system, which uses coal to heat millions of homes and offices in the city.
Harbin has a population of more than 10 million people. It lies in northeastern China, where cold winter weather can last up to six months. The main fuel* there is coal, because it is cheaper than other types of fuel.
Air pollution from burning coal can cause health problems like heart disease. During the smog crisis* in Harbin, the number of people taken to the hospital with breathing problems was 30% higher than usual.
The city government is trying to reduce its use of coal by adding more insulation* and better roofs and windows to buildings to reduce heating needs. It has also used cleaner fuel for cars and factories.
The roads and schools in Harbin had to be closed on October 21, 2013 because of  ____

A．the heavy rain

B．the strong wind

C．the serious smog

D． the terrible snow

There are many reasons for the air pollution EXCEPT____________.

A．farmers burn off old corn stalks and crop stubble

B．people use coal to heat millions of homes and offices

C．The smoke remains over the city because of low winds

D．Many buses and cars use cleaner fuel and so do factories.

What is the government trying to do when the air pollution get worse?

A．To offer cars new fuel.

B．To give people more masks.

C．To reduce its use of coal.

D．To ask people to stay at home.

What does the passage mainly tell us?

A．The serious air pollution in China

B．Coal-fired heating systems

C．The population crisis in Harbin

D．The reasons for heart disease