It was because of bad weather___the football match had to be put off.

答案是D
It is/was + 强调部分 +that +其他部分
这里强调的是天气不好这个原因.
至于为什么不选so that 因为：
so that　是表示以便,为了的意思；　
so.that是表示如此．．．以致的意思．　
so that是连在一起用的,表示结果．如：我读更多的书,以便我能赶上我的同学．I read more books so that I can catch up with my classmates.
so .that　是分开的,表示在什么条件下有的结果,that后加句子．
如：我太累了,以致我一吃完晚饭就去睡觉了．I was so tired that I went to bed as soon as I ate the supper.
对了,so that=in order to do sth