4.23.

A. 　 would be

B. 　 would have been

C. 　 must be

D. 　 must have been

A. 　 standard

B. 　 problem

C. 　 reason

D. 　 purpose

A. 　地球自转轴在外部空间上的变化,如“岁差”和“张德勒颤动”。

B. 　地球自转轴在外部空间上的变化,如“岁差”和“章动”。

C. 　地球自转轴在地球内部空间上的变化,如“岁差”和“章动”。

D. 　地球自转轴在地球内部空间上的变化,如“章动”和“第四种颤动”。

A. 　 there

B. 　 here

C. 　 where

D. 　 now

A. 　 century

B. 　 battles

C. 　 thing

D. 　 years

A. 　 though

B. 　 since

C. 　 but

D. 　 if

A. 　will be built

B. 　 will build

C. 　 was built

D. 　 built

A. 　 went

B. 　 has gone

C. 　 would go

D. 　 has been