各位前辈好 我想请问以下这句:
Authorities said that the possibility that the incident is linked to the poiso
ning in march of a former Russian spy is a "clear line" of their investigation
.
里面第一个that应该是名词子句当said的受词，但第二个that我就不清楚了，我基础还不
好感觉一圈又一圈转不出去，然后还有march后面的of是什么用法？
非常感谢各位 谢谢