Lowest organic matter at endpoint stations

Steps:

• Review concentration data for stations 1 through 5 from the graph or table.
• Identify values: Station 1 (lowest upstream), Station 5 (lowest downstream), with Stations 2-4 higher due to inputs.
• Compare pairs: Only 1 and 5 both have minimal levels.
• Confirm A matches the two lowest readings.

Why A is correct:

• Stations 1 and 5 register the lowest concentrations per the dataset, indicating minimal organic inputs at boundaries.

Why the others are wrong:

• B includes Stations 2 and 3, which show elevated levels from nearby pollution.
• C pairs Station 3 (high) with 4 (moderate), not both low.
• D combines Station 4 (moderate) with 5 (low), ignoring higher value at 4.

Final answer: A