You are studying gastroesophageal reflux therapy among two hundred premature infants all of whom are less than 30 weeks and being tube fed in a NICU. You measure the average intraesophageal pH upon entry into the study, at two weeks, at four weeks and at six weeks. The best method to analyze this data is:

A. repeat measures ANOVA

B. Pearson's correlation coefficient

C. regression using a model that includes time, volume of feeds and intraespohageal pH

D. Chi-square