—How about joining us in the summer camp?
—I wish I could, I have to practice for the piano test.
A. because
B. so
C. but
D. although
网友回答
A. because
B. so
(答案→)C. but
D. although
解析：because因为；so因此；but但是；although 虽然，尽管。句意：加入我们的夏令营怎么样？——但愿我能，但是我必须得为钢琴比赛练习。结合语境可知上下文是转折关系，故选C。