A student in a class did a good deeds without leaving a name  Four teachers, including A, B, C, D, etc  expressed their opinions to the four students in the class  A said: If this thing wasn't done by Zhang San, it would definitely be Zhao Liu did it  B said: If Zhang San did this thing, then Li Si or Wang Wu will do it too  C said: If Li Si doesn't do this thing, Wang Wu will not do it either  ;Zhao Liu would not be the one who did this
Ding said: This thing must have been done by Zhang San, and neither Li Si nor Wang Wu would do it
 Li Si 