For each of the following situations, explain the most likely cause of the error and error should be corrected.
a. After aspirating 300 ul with P1000, a small air space is seen at the end of the tip.
b. While aspirating 1 ml with a P1000, a small air bubble is observed rising t the top of the liquid inside of the tip.
c. A P20 tip-holder is stained with methylene blue.