Question

what change would most improve the usefulness of the graph?
replace the concentration descriptions with actual values.
plot contractions per second instead of contractions per minute.
remove the plotted points and just keep the line.
remove the name of the organism from the title.

Explanation:

The graph uses qualitative terms for salt - concentration ('Very low', 'Low', etc.). Changing these to actual numerical values would make it more precise and useful for scientific analysis. Plotting contractions per second instead of per minute doesn't improve the main issue of imprecise concentration values. Removing plotted points or organism name from the title doesn't enhance the graph's precision.

Answer:

Replace the concentration descriptions with actual values.