they are very tired, they feel happy because they’re finally finished their project.A. So

they are very tired, they feel happy because they’re finally finished
their project.
A. So
B. If
C. Although
D. But

A. SoB. If(答案→)C. Although D. But解析：So因此；If是否，如果；Although虽然，尽管；But但是。句意：尽管他们非常累，但是他们感到很高兴，因为终于完成了他们的计划。But和although这两个单词虽然含义与汉语中连词“虽然……但是”含义接近，但是一般不搭配使用，因为英语中单独使用一个即可表示转折关系。故选C。

对的，就是这个意思