Refer to the Diagram, Which Shows the Role of Vacuoles

Multiple Choice

Refer to the diagram, which shows the role of vacuoles in ciliate digestion. Which of the following is a plausible hypothesis to explain why the vacuole color returns to red?

A) The pH returns to basic because of increasing proton concentration.
B) The pH returns to basic because of decreasing proton concentration.
C) The dye from all food vacuoles coalesces into one vesicle destined for exocytosis.
D) Multiple food vacuoles at different stages of digestion fuse into a single vesicle.
E) The pH returns to acidic because of an increase in salt concentration.