关于数字证书的说法中，错误的是（）。 A.数字证书是一个经证书认证机构（C A.数字

中央银行投放基础货币的渠道有（）。

A.对金融机构的再贷款

B.收购金银外汇

C.购买政府债券

D.对工商企业贷款

E.对个人贷款

Have you ever wondered why birds sing? Maybe you thought that they were just happy．After all, you probably sing or whistle when you are happy．

Some scientists believe that birds do sing some of the time just because they are happy．However, they sing most of the time for a very different reason．Their singing is actually a warning to other birds to stay out of their territory．

Do you know what a "territory" is? A territory is an area that an animal, usually the male, claims as its own ．Only he and his family are welcome there ．No other families of the same species are welcome．Your yard and house are your territory where only your family and friends are welcome．If a stranger should enter your territory and threaten you, you might shout．Probably this would be enough to frighten him away．

If so, you have actually scared the stranger away without having to fight him．A bird does the same thing．But he expects an outsider almost any time, especially at nesting （筑巢） season．So he's screaming （高声尖叫） all the time, whether he can see an outsider or not．This screaming is what we call a bird's song, and it is usually enough to keep an outsider away．

Birds sing loudest in the spring when they are trying to attract a mate and warn others not to enter the territory of theirs．You can see that birds have a language of their own．Most of it has something to do with attracting mates and setting up territories．

小题1:Some scientists believe that most of the time birds' singing is actually

A．an expression of happiness

B．a way of warning

C．an expression of anger

D．a language of their own小题2:What is a bird's "territory"?

A．A place where a bird may shout at the top of its voice．

B．A place where other bird families are not accepted．

C．An area for which birds fight against each other．

D．An area which a bird considers to be its own小题3:Why do birds keep on singing at nesting season?

A．Because their singing helps frighten outsiders away．

B．Because their singing helps get rid of their fears．

C．Because they want to find outsiders around．

D．Because they want to invite more bird friends．小题4:How does the writer explain birds' singing?

A．By comparing birds with human beings．

B．By reporting experimental results．

C．By describing birds'daily life．

D．By telling a bird's story．

消防员灭火防护胶靴经总质量为（）g的刀头切割后不被割穿。

A.2000.0

B.800.0

C.1000.0

D.1500.0

下列药物中，不是诱发排卵药是（）.

A.HMG

B.氯米芬

C.HCG

D.GnRHa

E.三苯氧胺

（）的工作价值取决于创造力、解决问题的能力及专业职能。

A.生产人员

B.研发人员

C.销售人员

D.高级主管人员