4．
The Zebra Finch：An Owner's Guide to a Happy Healthy Pet
The zebra finch，a native of Australia，is a popular domestic pet in the United States．The bird has many attributes （特性） which allow it to be kept at home，though there are also a few negative aspects．The attributes are nest-building，breeding and a lively attitude．The potential negatives are over-breeding and the wildness of the birds．
One of the main attributes of zebra finches is their ability to breed．They are the rabbits of the domestic bird world．Once you have two birds，male and female，you will soon have six，as they breed quite easily and have strong babies，usually four at a time．An added attribute is their ability to build their own nests．You can place branch in their place along with some kind of structure，and they will create a nest on their own．It's very pleasant to see the ways males and females divide some labors and share others，and the babies grow up quickly．Overall，zebra finches are energetic birds，and they can make every place where they live delightful lives．
On the negative side，they will breed and in-breed．Often，in-breeding does little harm and does not cause genetic defects （缺陷），as happens more often in other species．However，no one can tolerate just any population level．One has to either remove their nests altogether，which basically removes their personal living place，or check for eggs regularly once a week （the gestation period is 13days，so even a one-week neglect can lead to births）．Eggs can be replaced with false plastic eggs，and this prevents females from laying too many．If they do lay too many，they will die from mineral loss．Since these birds do not tame well，removing eggs can be an unpleasant process of repeatedly invading their personal space．
Overall，it is unfortunate that zebra finches are inexpensive birds due to their high level of breeding．They require considerable care to live happy lives．The best care-takers are true avian fanciers-people who have appropriate space for the nests and enough time to allow them to nest-build and breed without over-breeding．
70．What is the passage mainly about？C
A．Zebra finches over-breed by nature and its consequent ill effects．
B．Only people who love birds can take care of Zebra finches．
C．Domestic zebra finches require a lot of care to live happy lives．
D．Zebra finches never become completely tame．
71．By saying"They are the rabbits of the domestic bird world"，the writer means that both rabbits and Zebra finchesA．
A．have good ability to breed
B．are difficult to be raised
C．live delightful lives
D．share responsibilities
72．In paragraph 3，the word"gestation"probably meansD．
A．the period when eggs remain fresh
B．the time when finches build up their nest and lay eggs
C．the time required for the parents to create a nest
D．the time required for baby birds to develop and to be born
73．According to the passage，attributes of domestic zebra finches includeB．
A．their rareness and easiness to be tamed
B．their nest-building，sharing of responsibilities and delightful personalities
C．their in-breeding，which does not cause as much genetic harm as in other species
D．the fact that they are from Australia and have difficulty in adapting themselves．
