23.Tom had a bad cold..23.Tom had a bad cold.___is why he didn't come to school.\x0b A.It B.That C.This D.There和区别

23.Tom had a bad cold..23.Tom had a bad cold.___is why he didn't come to school.\x0b A.It B.That C.This D.There和区别
23.Tom had a bad cold..
23.Tom had a bad cold.___is why he didn't come to school.\x0b 
 A.It   B.That   C.This   D.There
和区别

23.Tom had a bad cold..23.Tom had a bad cold.___is why he didn't come to school.\x0b A.It B.That C.This D.There和区别
that

习惯用B

A, cold后面是句号， 说明后面是一个独立的句子，用that的话没有主语，两个都是代词功能，it指代上面的结果进行说明。

B. That