why is D wrong..?
(D) Blood pressures are low among the Yoruba, who, throughout their history, have been situated far inland from sources of sea salt and far south of Saharan salt mines.
In order for the researchers hypothesis to hold true there has to be an environmental scarcity of salt in Africa. This contradicts the hypothesis by stating that there are multiple sources of salt in Africa (sea salt and salt mines).
Actually this doesnt contradict at all. Notice that these sources are "Far."
I agree though, D is not as strong as A.
A essentially says that b/c there is lots of salt, blood pressure is low for those who have been around it for awhile.