题目内容：

Deliberately making a road icy sounds like a method for disaster, but in 16th-century China it helped things run smoothly. Repairs to the Forbidden City in Beijing in 1557 called for huge stones from a quarry(采石场) more than 70 km away. The biggest was the 300-ton “Large Stone Carving.” Such stones were too heavy for any cart, and too fragile for rollers. The builders adopted a wise alternative approach to carry the heavy stone.

They dug a series of wells, spaced a few hundred metres apart, along the route to the quarry. Then, in the depth of winter, when temperatures reached around -4℃, buckets of water were poured on to the dirt track, transforming it into an ice road.

The stone blocks were pushed along the road on wooden sledges (雪橇). Modern engineers have calculated that it would take 1,500 workers to drag a sledge on the dirt road, but only 300 on ice. Ancient tests suggested the ice was made slippery with more water; this reduced the friction further and just 50 men could pull a sledge. This technique only works when the temperature is also close to zero, otherwise the film of water freezes too quickly.

The researchers at Princeton University estimated that the blocks could be moved at six metres a minute, and the journey could be completed in 28 days. This would be well before the spring when the ice would melt.

It was once suggested that similar ice-sledges transported Stonehenge stones, but the ground that had a lot of holes and comparatively mild conditions probably rule this out.

1.Why did people dig some wells along the road to the quarry?

A. They wanted to build frozen roads.

B. They wanted to break up large stones.

C. They wanted to make the dirty track clean.

D. They wanted to get a lot of holes on the road.

2.What did people do to reduce the friction?

A. They made stone blocks much smaller.

B. They poured more water on the ice road.

C. They waited until the temperature was very low.

D. They asked more than 1,500 workers to clean the dirty road.

3.How did the researchers at Princeton University think of Stonehenge stones?

A. They were not likely to be carried on the icy road.

B. They had a longer history than stones in Beijing.

C. They were carried for over twenty-eight days.

D. They were broken up in the depth of winter.

4.What does the author intend to tell us in the text?

A. Making a road slippery on purpose may be bad idea.

B. The mild weather helped to carry Stonehenge stones.

C. Stonehenge stones were too heavy to carry.

D. Ancient Chinese transported huge stones wisely.