For an evidence-based explanation question, isolate every part of the observation that the correct choice must address. Here, a successful explanation must account for the initial advantage of one group, the selective removal of certain threads, and the subsequent reversal. Reject choices that explain only a general decrease or only one stage of the experiment.
Hints
- Hint 1
Track the comparison
Consider how the relative performance of the two groups changes before and after the thickest threads are clipped.
- Hint 2
Look for a complete explanation
The best choice must explain not only why clipping weakens the mussels but also why it affects one group's ranking more dramatically.
Step-by-step
- Step 1
Identify the pattern requiring explanation
Before clipping, the surge-exposed mussels resisted detachment better despite having fewer threads. After the thickest one-fifth of the threads were clipped, those mussels resisted detachment less effectively than the continuous-flow mussels.
- Step 2
Determine what the evidence must explain
A complete explanation must account for both the surge group's initial advantage and its larger loss of anchoring strength when the thickest threads were removed.
- Step 3
Select the explanation that fits both results
If the surge-exposed mussels concentrated their byssal material in a few exceptionally strong threads, those threads could provide the initial advantage. Clipping them would remove a disproportionate share of the group's anchoring strength, while the continuous-flow group's more evenly distributed strength would be less affected. Therefore, the correct answer is Surges prompt mussels to concentrate byssal material in a few exceptionally strong threads, while continuous currents prompt a more even distribution among threads.