The stem says:

People who originated from people who had less access to salt, are predisposed to develop high blood pressure when confronted with high salt diets.

this is rephrased in A; those Africans whose ancestors had no scarcity of salt don't develop high blood blood pressure when confronted with high salt diets.

One more vote for A.

Nice explanation all about.

Researchers have hypothesized that this predisposition in westernized Blacks may reflect an interaction between western high-salt diets and genes that adapted to an low salt env.

we are looking for an answer that says that if salt was in plenty...and there was no reason genes had to adapt...then BP is less of a issue A is right on the money. [color=blue]

Joining the A gang.
B and C are out of scope.
D andE negate the hypothesis.

D

paraphrase:
Black Americans are twice more likely to get BP than White Americans.
This is same for western Black Africans compared to White Africans
Hypothesis: High salt diet v/s the genetic makeup which is adapted (in western Blacks) to scarcity of salt and hence the BP problem.

Cause & effect: high salt diet, for people adapted to low salt diet causes BP more often in the Black pop than White pop

This is a "strengthen" question.

1. Which of the following statements about present-day, westernized Black Africans, if true, would most tend to confirm the researchers’ hypothesis?

(A) The blood pressures of those descended from peoples situated throughout their history in Senegal and Gambia, where salt was always available, are low.
--> here the BP for the decendents of people who eat regular salt diets is low, so if these folks eat a high salt diet, would they tend to have BP problems?

(B) The unusually high salt consumption in certain areas of Africa represents a serious health problem.
--> we know the diet but we dont know the availability of salt here and hence their genetic makeup.

(C) Because of their blood pressure levels, most White Africans have markedly decreased their salt consumption.
--> question is about the diet and BP levels for the Black Africans

(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.
--> here the salt was never available in plenty, and hence they adapted themselves to low salt diet, hence they have a lower BP. If they are now subjected to high salt diet, then they would tend to get BP.
This goes with the passage above and strengthens the case.

(E) No significant differences in salt metabolism have been found between those people who have had salt available throughout their history and those who have not.
--> contradicts the hypothesis