To me the necessity of zoos in cities is only found_______their educational purpose.

     In 1997, the geoscientist Brian Toon and colleagues found that a space rock half a mile wide would produce an explosion that releases the energy equivalent of up to 100,000 million ions (Mt) of TNT. And a meteorite a mile in diameter might send enough pulverized rock into the stratosphere to block out sun-light and cause global cooling.

The object that killed off the dinosaurs was probably seven or eight miles wide, says Jay Melosh, a planetary physicist at Purdue University. Its impact would have ejected a dust smoke that spread clear around the planet and rained blazing-hot on to forests, igniting them. “The dinosaurs probably broiled to death,”he says.

Such a collision today would kill billions of people. Those who didn’t perish in the initial blast or the fires that followed would face long odds of finding sustenance. “People are going to starve to death,” Toon says. Still, a few would likely weather the apocalyptic storm. For a collision to wipe out the human race altogether, Toon estimates it would take a 60-mile-wide meteorite. He says, “That would burn everybody to death.”

My View on Robots

However, much of industry is concerned with batch production where perhaps one type of item is made during the morning and another during the afternoon. Human beings are very good in this environment. From a robotic point of view, they are light mobile structures with exceptionally good sensory perception and intelligence far above that of any current robot.

The car accident happened because the traffic lights were_______.

Hydrogen is the fuel of the future. Unfortunately, one problem (31): Hydrogen is a gas and cannot easily (32)pumped into a tank like gasoline. Storage(33)the form of solid hydrides, chemical compounds of hydrogen and a metal (34)semimetal, are good storage materials in principle, but have not been well suited (35)automotive applications. An American research team at the Ford Motor Company in Dearborn and the University of California, Los Angeles, has now (35) a novel hydride that could be a useful starting point for the development of future (37)hydrogen-storage materials. As Jun Yang and his team have(38)an “autocatalytic” reaction mechanism causes the composite made(39)three different hydrides to rapidly release hydrogen at lower temperatures and(40) dangerous by-products.

replete with

in memory of

stem from

opt for

within reach of

1、正确的决定来源于正确的判断。

2、李教授想在大学附近租一套公寓。

3、上水果前，每位用餐者都己经吃得很饱了。

4、选择职业时，父亲让我拿主意，我选择了教师职业。

5、为了纪念在这次战斗中牺牲的三位英雄，村民们修建了一座纪念碑。

He_______his imagination and personal experiences to write this novel.

Students were still ________the lecture in the hall when the bell rang.

Most trains would________passengers during the holiday season.

All he had was money, which he_______his retired grandfather.