Consider these three variables: finishing times in a marathon, number of university dining hall meals eaten in a semester on a three-meala- day plan, and scores on a scale of extroversion. 

a. Which of these variables is most likely to have a normal distribution? Explain your answer. 

b. Which of these variables is most likely to have a positively skewed distribution? Explain your answer, stating the possible contribution of a floor effect. 

c. Which of these variables is most likely to have a negatively skewed distribution? Explain your answer, stating the possible contribution of a ceiling effect.