—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
某蛋白质分子由l00个氨基酸组成,含2条肽链,则在氨基酸脱水缩合形成该蛋白质的过程中产生的水分子个数为
按要求改写句子。