I wouldn't recommend thinking about this in terms of strengthening an argument, because the text in this case isn't really an argument. The author doesn't present a conclusion, so there's nothing to strengthen or weaken. You could, however, think of B as heightening the discrepancy. If barnacles attach best in areas of weak tidal currents, then it's even
more mysterious that the juveniles in these areas aren't covered in barnacles. We could think of A in similar fashion, since it seems to rule out an explanation, but it doesn't seem terribly relevant, since the areas we're wondering about don't have strong tidal currents.
findingmyself
How the below two Trap answers are negated: Here is my logic
(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.It is actually strengthening the conclusion but not explaining why Paradox, This answer will be my choice for strengthening the argument
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest. My paradox is not explained since what is required is why a large population of banacles are not attached to shells. Readily attached is not helping to explain the paradox.