填空。 Suppose, for example, that a teacher tells her students they each must do one hundred maths problems 1 coming to school the next day. The 2 complain about so much home study. But one student does not 3 anything at all. That student is an eager beaver. He 4 to work out maths problems, and does not mind all the 5 . Another eager beaver works as a salesman for a business. He 6 arrives at the office before anyone else, and is the 7 person to leave. The man works hard, because he 8 his job. He is a true “eager beaver”. The expression 9 the name of a hardworking animal, the beaver. Beavers are 10 creatures. They are like mice and rats, but much 11 . Some weigh more than twenty-five kilograms. Beavers have a large, black, flat tail to 12 them swim. They also have thick brown hair or fur to keep them warm in cold 13 .They have front teeth 14 enough to cut down large trees. Beavers spend a lot of time in the water, building dams（堤，坝） to form little 15 or pools. They work hard to cut down trees, 16 branches and put them across streams. They use their tails to pack mud on the branches to make the dams solid. 17 other animals work so hard. In fact, for two hundred years or more, the beaver was the most valuable animal in North America. And thus most of the beavers were killed. For a time, they were in danger of 18 completely. But laws were passed to 19 the beaver, and today, the 20 is rising. And, like the animal, the expression “eager beaver” is in no danger of dying out. (     )1.A.when (     )2.A.children (     )3.A.do (     )4.A.loves (     )5.A.physical labour (     )6.A.seldom (     )7.A.most eager (     )8.A.has to do (     )9.A.comes from (     )10.A.tailless (     )11.A.smaller (     )12.A.make (     )13.A.rain (     )14.A.fearless (     )15.A.lakes (     )16.A.grasp (     )17.A.All (     )18.A.running away (     )19.A.feed (     )20.A.condition B.instead of B.teachers B.speak B.refuses B.easy job B.sometimes B.last B.needn’t do B.is separated from B.good-looking B.larger B.watch B.land B.smooth B.pipes B.suck B.Most B.disappearing B.raise B.population C.as C.parents C.ask C.hates C.homework C.always C.only C.loses C.is given to C.strange-looking C.quicker C.let C.water C.quick C.gardens C.remove C.Many C.missing C.catch C.quality D.while D.headmasters D.say D.fails D.housework D.never D.first D.enjoys D.has nothing to do with D.kind-hearted D.better D.help D.ice D.sharp D.parks D.climb D.Few D.losing D.protect D.safety