Critical Reasoning

Traces of cultivated emmer wheat have been found among the earliest agricultural remains of many archaeological sites in Europe and Asia. The only place where the wild form of emmer wheat has been found growing is a relatively narrow strip of southwest Asia. Since the oldest remains of cultivated emmer wheat yet found are from village sites in the same narrow strip, it is clear that emmer wheat was first domesticated somewhere in that strip.
Which of the following, if true, most strengthens the argument?
"¢ The present-day distribution of another wild wheat, einkorn, which was also domesticated early in the development of agriculture, covers a much larger area of southwest Asia.
"¢ Modern experiments show that wild emmer wheat can easily be domesticated so as to yield nearly as well as traditionally domestic strains.
"¢ At
"¢ the time when emmer wheat was first cultivated, it was the most nutritious of all the varieties of grain that were then cultivated.
"¢ In the region containing the strip where wild emmer wheat has been found, climatic conditions have changed very little since before the development of agriculture.
"¢ It is very difficult, without genetic testing, to differentiate the wild form of emmer wheat from a closely related wild wheat that also grows in southwest Asia

I cant understand how D strengthens the answer? Can someone explain it .