If he did not learn erhu performance, Xu Ping would not be able to study folk music theory. If he likes folk instruments, he would choose to study erhu performance as a major. If he does not like folk instruments, he would do folk music theory research. Can Xu Ping be introduced from this? ['Studying folk music theory.', 'Learn to play erhu.', 'Do not learn to play erhu.', 'Not studying folk music theory.']