A sandstorm, the first this year, turned the Beijing sky pale yellow on Sunday.

"The dust slightly polluted the air and reduced visibility on Sunday, but it did no harm to the crops," head of the Beijing meteorological bureau (BMB) Guo Hu told reporters yesterday.

The sandstorm was caused by a "sudden cold front, which blew in dust from outside the capital," he said.

The storm affected an area of about 160,000 sq km, including Beijing and its surrounding Hebei and Shandong provinces, Guo said. He added that another sandstorm may hit the capital in the next 10 days.

"But during April there are a lot of chances for sandstorms," he added.

According to BMB's forecast, the city will see "no less than six dusty days this spring, fewer than the annual average of about 10 days".

Guo said dust storms in China were divided into four levels depending on its intensity - floating dust, flying sand, sandstorm, and severe sandstorm.

According to statistics with the BMB, in the last few decades, flying sand days and sandstorms had seen a considerable decrease. On average, there were 33 flying sand days every year before 1980. This has decreased to nine days since 2000. Sandstorms, too, have been rare since 1996.

The country's first wide-range sandstorm hit large parts of Northern China, including Gansu, Ningxia, Hebei, Henan, Shanxi, Shannxi, Shandong, Tianjin and Inner Mongolia last week.

Chances of another sandstorm are high in Gansu, Ningxia and Inner Mongolia, the China Central Meteorological Station said.

Questions:

1. What caused the recent sandstorm?

2. What areas did the sandstorm affect?

3. Name the four levels of dust storms, depending on intensity.

Answers:

1. A sudden cold front, which blew in dust from outside the capital.

2. Beijing and its surrounding Hebei and Shandong provinces.

3. Floating dust, flying sand, sandstorm, and severe sandstorm.