"long term effects"

My question is about whether my logic is correct, So the stimulus does introduce the idea of long-term effects, and because answer choice b allows for the possibility of time to create a difference in the study's observations, it circles back to this idea of long term effects and is thus directly challenging the angle of the study/stimulus and weakening the conclusion by bringing in the possibility that perhaps the long term effects were not observed because it takes time for the oil to settle on the ocean floor and thus have an opportunity to cause any effects it might onto the animal life on the bottom of the sea. I didn't see any mention of 'long term effects' in any of the explanations or previously answered questions, so I wanted to ask if this line of logic is not wrong to follow?