Final answer:
An excessively pink stain can cause prolonged washing time, mounting coverslips before they are dry, and too high acidity of the stain. The correct option is d.
Step-by-step explanation:
An excessively pink stain can cause all of the above (prolonged washing time, mounting coverslips before they are dry, and too high acidity of the stain).
If a stain is excessively pink, it means that there is an excess amount of stain present on the slide. This can lead to prolonged washing time as the excess stain needs to be rinsed off.
Additionally, if coverslips are mounted before the stain is completely dry, the excess stain can seep out and contaminate the microscope slide, causing it to become pink. Lastly, if the stain is too acidic, it can affect the staining process and the overall quality of the stain. The correct option is d.