题目选项分析

A sudden increase in the production of elephant ivory artifacts on the Mediterranean coast of North Africa occurred in the tenth century. Historians explain this increase as the result of an area opening up as a new source of ivory and argue on this basis that the important medieval trade between North Africa and East Africa began at this period.

Each of the following, if true, provides some support for the historians' account described above EXCEPT:

【选项】The many surviving letters of pre-tenth-century North African merchants include no mention of business transactions involving East Africa.