The gill lining of lobsters in which the disease-causing par

Let recap what we know from the paragraph:

Gill lining regenerates every 30 days
An. haemophila CANNOT move from infected gill lining to new gill lining
-->Inference: An. haemophila must reinfect lobsters' gill lining every 30 days
An. haemophila LEADS TO gill discoloration
-->Conclusion: If lobsters move to water without An. haemophila, after 30 days their gills will have regenerated, and there will not be An. haemophila to reinfect and discolor their gill lining. THUS, any gill discoloration at this point is NOT CAUSED BY An. haemophila infection.

We want to WEAKEN this argument. This means we want to strengthen the argument that gill discoloration after 30 days in parasite-free water COULD BE CAUSED BY an An. haemophila infection. Since An. haemophila must reinfect lobsters' gill lining every 30 days, we need to find a way for the lobsters to become reinfected, despite being in water without An. haemophila.

A. The presence of other parasites doesn't really matter — we only care about one parasite: An. haemophila. If anything, it strengthens the idea that discoloration could be caused by a different parasite that sticks around longer than 30 days. Eliminate.
B. This statement is about "lobsters that remain in parasite-rich waters". We only care about lobsters that have been moved to parasite-free waters. Eliminate.
C. We want to know about gill discoloration, not digestive and respiratory distress. Similarly, this doesn't tell us anything about how lobsters become reinfected. Eliminate.
D. If An. haemophila moved to the lobsters' stomach during the 30 days, the gill lining could regenerate, then An. haemophila could reinfect the new gill lining AFTER 30 days. This works!
E. If lobsters who have already had An. haemophila are able to resist reinfection, that makes it less likely that the gill discoloration in our previously infected lobsters is due to reinfection. This STRENGTHENS the argument. Eliminate.

The correct answer is D. Restating the argument in your own words and making a prediction can help a lot with eliminating answer choices.