题目：
We have received your letter of September 12，（）we are glad to know that you are interested in our electric heaters.
A.which
B.at which
C.from which
D.in which
答案：
参考答案：C
We have received your letter of September 12，（）we are glad to know that you are interested in our electric heaters.
A.which
B.at which
C.from which
D.in which
参考答案：C
