问题补充:
—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
答案:
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。