The salmon(大麻哈鱼) is a very strange fish.　 It is born in a river.　 But the young salmon takes 2 years to swim down the rivers towards the Pacific Ocean.　 For another 2 years it lives in the sea and becomes full grown.　 Then it returns to the river where it was born.

　　A grown-up　 salmon weighs about 25 pounds and is nearly three feet long.　 The female salmon will not lay the eggs(产卵) in the Pacific Ocean.　 When it is almost time to lay them, both male and female salmon begin a great journey. 　Each salmon is heading for the river where it was born.　 A salmon may be a thousand miles from where its life began, yet it is able to return to that place.

　　As the salmon swim, larger fish attack(袭击) them.　 The salmon are food for some other fish.　Some are caught by fishermen.　 The salmon that are left keep swimming.

　　After they enter the rivers, they head upstream(向上游).　 If rocks and waterfalls(瀑布) are in their way, the salmon leap(跳) over them.　 A salmon can leap up a fall as high as ten feet.　 It leaps by swimming at full speed under water, then rising to the surface.　 Almost the whole body of a salmon is made of muscle(肌肉).　 It is these powerful muscles that make the salmon fit for fast swimming, turning quickly, and leaping high out of the water.

　　Some reach their river in summer, others in the early autumn.　 They have come hundreds, even thousands of miles and it has taken them weeks and months.

　　 49. The young salmon was born _____ and grows up _____.

　　  A. in a river...in the river　  B. in a river...in the sea

　　  C. in a sea...in the sea　  D. in a sea...in the river

　　50. _____, both male and female salmon will return to where they were born.

　　  A. When it is almost time for a female salmon to lay eggs

　　  B. After the female salmon has laid the eggs

　　  C. When they weigh 25 pounds and are nearly three feet long

　　  D. After they have lived in the Pacific Ocean for 4 years

　　51. On their way back to the birth place, _____ salmon are eaten by larger fish and _____ caught by fishermen.

　　  A. most...the others　  B. some...the others

　　  C. most...the rest  D. some...others

　　A few birds care for their eggs without sitting on them． In Australia, the male mallee fowl builds an incubator nest out of rotting vegetation covered with soil． As the vegetation decays, it gives off heat． The male pokes his beak into the middle of the pile and tests the temperature． If the temperature isn't an even 92° Fahrenheit, he adjusts it by adding or removing soil．

　　The female spends most of her time watching him, but sometimes she helps him． About once a week she lays another egg inside the nest．

　　The pair maintain their nest for several months． When the chicks begin to hatch -- one by one -- they dig their own way out of the nest and dash into the bush to fend for themselves． Although mallee fowl take great care of their eggs, no mallee fowl has ever been seen with a brood of chicks．

1．Most birds' eggs are hatched by heat from_______．

A．the sun's raysB．incubators

C．their parents' bodies　　D．None of the above

2．The heat in a mallee fowl nest comes from the_______．

A．beak of the male　　B．vegetation decaying under the soil

C．rays of the sun　　 D．body of the female

3．Temperature adjustments within the nest are made by_______．

A．adding more soil B． removing soil C． Either A or B　　D． Neither A nor B

4．The article does not tell_______．

A．how the male removes soil from the nest　　B．why the female seldom helps the male

C．why the nest must be a certain temperature D．Any of the above

5．Mallee fowl eggs hatch_______．

A．all together　　 B． individually

C．in twos or threes D． in small clutches

6．When a chick hatches, it______．

A．must dig its way out of the nest B．can fend for itself

C．needs assistance from its parents D．Both A and B

7．A brood of mallee chicks is never seen because the female lays only one egg every_______．

A． dayB． weekC． fortnightD． month

8．Because of the way mallee fowl care for their eggs, the_______．

A．adults cannot live in the nest themselves B． adults do not need to work hard

C．female is kept very busy　　 D． male has no work to do