IMO D. The argument: East African & North African (near Mediteranean coast) began trading to each other no earlier than 10 century

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 following, if true, provides some support for the historians’ account described
above EXCEPT:
A. In East Africa gold coins from Mediterranean North Africa have been found at a
tenth-century site but at no earlier sites -->gold coins mean business, so this strengthens that their business - East & North Africa near Mediteranean, began no earlier than 10-century
B. The many surviving letters of pre-tenth-century North African merchants include
no mention of business transactions involving East Africa --> this eliminates any possibility that North & East have trading to each other earlier than 10 century, thus strengthening the argument
C. Excavations in East Africa reveal a tenth-century change in architectural style to
reflect North African patterns -->strengthen. From 10 century, East African has been influenced by North African's architecture. This means they began a relation at 10 century, and it was likely business relation
D. Documents from Mediterranean Europe and North Africa that date back earlier
than the tenth century show knowledge of East African animals -->this mentions about pre 10 century but shows no relations between North African Mediteranean coast & East Africa. It neither strengthens nor weakens, thus the best
E. East African carvings in a style characteristic of the tenth century depict seagoing
vessels very different from those used by local sailors but of a type common in
the Mediterranean --> strengthen. At 10 century, East African had seagoing evidences related to that of Mediteranean coast, and because those can be of the Mediteranean coast of North African, so it connects East African & North African mediteranean coast