题目内容：

    Not many organisms can survive in this severe environment, the Sahara Desert, where daytime temperatures can reach 140 degrees Fahrenheit. But an insect called the Saharan silver ant grows well. They rush out onto the sand from their protected nests to gather up the bodies of insects that have died from the heat.

“The hotter the day, the more insect bodies they will find. The more food they have.” said Sarah Pfeffer, an animal behaviorist at Ulm University in Germany. She says that to avoid sinking into the Saharan sand, where they could meet the same fate（命运）as their lunch, silver ants have to be fast.

To document just how quickly the ants move, Pfeffer and her colleagues set up high-speed cameras above a channel between the entrance to the hungry ants’ nest and a food source. The researchers recorded top speeds approaching 35 inches per second.“But if you really look at how big the animals are and you calculate the body length per second, you will come up with a walking speed that is an astonishing 108 body-lengths per second.”That figure makes them the fastest known ant on the planet. By comparison, cheetahs(猎豹）top out at about 16 body lengths per second. The videos showed how the ants achieve such amazing speeds. As they accelerate, their leg movements become synchronized(同步). They increase their running length by bringing all six feet off the sand at once, which Pfeffer describes as a gallop. “Really all legs are lifted from the ground. They are in the air, but it’s not jumping. It’s a very smooth run that they have.”

A closely related ant called Cataglyphis fortis only reaches about 24 inches per second, or two-thirds of the silver ant's max.

The Saharan silver ants' speeds may be impressive, but two insects are even faster. The Califormia coastal mite (壁虱) and the Australian tiger beetle, both of which also grow well at near-deadly temperatures. It seems that to beat the heat, it pays to be fleet.

1.What does the underlined word "they" refer to?

A.The insects. B.The silver ants.

C.Pfeffer and her colleagues. D.The high-speed cameras.

2.How long is a Saharan silver ant?

A.About 0.14 inches. B.About 0.08 inches.

C.About 0.22 inches. D.About 0.32 inches.

3.How do the ants accelerate while running?

A.By jumping smoothly. B.By lifting all their legs.

C.By sinking into the sand. D.By flying in the air.

4.Why does the author mention another two animals in the last paragraph?

A.To introduce two speedy animals.

B.To present the near-deadly environment.

C.To show high temperature makes fast speed.

D.To indicate silver ants rank third in speed.