I sent the letter early that morning _______ she got it that

I sent the letter early that morning _______ she got it that afternoon.
A.in order that B.so that C.for purpose that D.in order for
您好!此题分析如下：不对请指正.
in order that 和so that 都表“目的”；故A;B都对.
有人说,“它俩意思一样,后面接法也相同,都接一个情态动词,所以这个题目不能理解为"目的"了,而只能理解为"结果"了,故答案是so that.这个题目要逆向思维.”应如何理解?如何翻译?