Along the letter was the promise he decided to help us with our work.
A. what
B. which
C. that
D. it
网友回答
A. what
B. which
(答案→)C. that
D. it
解析：考查同位语从句。同位语从句he decided to help us with our work.解释the promise的内容。结合句意可知C正确。句意：随着那封信得是他的诺言，那就是他决定帮助我们的工作。