We are extremely sorry about this delay,（ ）you will realize was

We are extremely sorry about this delay,（ ）you will realize was due to circumstances beyond our control.
A、that
B、what
C、if
D、which
【正确答案】：D
【题目解析】：根据句子意思，which在句中做代词使用，指代前半句中的delay。