At a certain academic conference, it was found that Professor Zhang knew everyone who knew Dr. Li; as long as it was not known to some people, Researcher Zhao knew all of them; Xiao Wang, a new graduate student who participated in the conference, did not know anyone. From the above statement, which of the following can be concluded? ['Professor Zhang and Researcher Zhao know each other.', 'Professor Zhang knows Professor Zhao, but Professor Zhao does not know Professor Zhang.', 'Professor Zhang and Researcher Zhao do not know each other.', 'Professor Zhang does not know Professor Zhao, but Professor Zhao knows Professor Zhang.']