Comparison of the growth rings of ancient trees enables scientists to determine from a piece of timber the year in which the tree used for the timber was felled.Hence， by analyzing the growth rings in timber surviving from ancient buildings， archaeologists can determine precisely when those buildings were constructed.

Which of the following is an assumption on which the argument depends？

（A） The timber used for construction purposes in ancient times was made from very old trees.

（B） The timber that was used in ancient building construction had not， prior to being used in the construction of the buildings， lain unused for an indeterminable amount of time.

（C） The growth rings of any tree felled in a given year are identical to the growth rings of any other tree felled in that year.

（D） The oldest of the ancient buildings that survive to the present day were constructed of the most durable woods.

（E） Ancient builders did not use more than one type of wood for the construction of a given building.

答案：B