# Comparing proportions of 2 groups

I want to compare the proportions of 2 groups statistically. My data look like this (the actual dataset contains 700,000 rows):

GROUP A GROUP B GROUP C
0.7     0.2     0.1
0.3     0.4     0.3
0.2     0.23    0.57
…       …       …


So every row sums to 1. Moreover, the data are paired in the sense that every row is a proportion for the same subject.

Now I want to know whether the average proportion of GROUP A is significantly higher than the average proportion of GROUP B. Does anybody have an idea about the appropriate test for this? I could not find a specific test for this problem so far on the internet. I assume that a regular t-test is not appropriate in this case because I'm working with proportions.