Claudia is interested in knowing which figure skater competing in the Olympic Games is most favored to win a gold medal. To sample the students in her school, she prepares a list of all of the boys and girls in the school and randomly chooses a sample from each group so that the size of each group is proportional to the number of boys and girls in the school. Which sampling method did Claudia use? A. simple random sampling
B. stratified random sampling
C. systematic random sampling
D. simple non-random sampling