阅读下面短文，从每题所给的四个选项中选出最佳答案.Ifyoucanfindatreewhichhasbeencutdownyouwillseemanyringsorcirclesonthebaseofthetrunk（树干基部）.Bylearningtoreadthese

题目详情

阅读下面短文，从每题所给的四个选项中选出最佳答案.

　　If you can find a tree which has been cut down you will see many rings or circles on the base of the trunk （树干基部）. By learning to read these rings you can find out the tree's life.

　　The number of rings tells you how old the tree is. Each year new wood is formed on the outside of the tree. This new wood is light in colour when the tree is growing in spring and summer and dark in winter when the tree is not growing much. So if you count the rings in dark-or-light-coloured wood you can often find out how old the tree is.

　　You can also tell which years have been good years and which years have been bad years. When the light-coloured rings are very wide it means that the tree has been growing quickly that year. If the light rings are narrow it has been growing slowly. If the rings on a tree trunk were greatly magnified （放大） you would be able to see why the rings are light-coloured when the tree is growing quickly and dark-coloured when the tree is growing slowly. The tree trunk is made up microscopic tubes （毛细管） like long pipes carrying water from the soil through the trunk and up to the leaves. They are wide and thin-walled when the tree is growing quickly and they are carrying a lot of water. They are narrow and stuck together when the tree is not growing so quickly.

　　When a tree is old the tubes in the centre of the tree don't carry water. The walls of the tubes have become thick with materials which have stuck along them over the years forming a kind of wood called “heartwood”. This kind of wood is darker in colour than the young growing wood on the outside of the tree.

　　You don't very often see whole tree trucks which have been cut across. But once you learn to read a cross section （横断面）of the wood you can see much more in wood which had been used to make boxes houses and other things.

　　In most wood instead of seeing the trunk cut across you are seeing it cut along its length. Because you don't see the whole tree you can't tell how old it was.

（1）The writer says you can tell the age of a tree by ________.

[　　]

A. the number of rings in its trunk

B. the size of the base of its trunk

C. the colour of its rings

D. the rings on the outside of the tree

（2）When the wood of a tree is mostly light in colour this means that the tree ______.

[　　]

A. grew slowly

B. grew quickly

C. only grew in winter

D. only grew in summer