(2) Yes. Article 24 of the Patent Law stipulates that the invention, utility model and design for which a patent is applied shall not lose its novelty if it is exhibited for the first time in an international exhibition sponsored or recognized by the China government within six months before the date of application. A participated in the exhibition in June, 28, and filed a patent application in September, 28, within six months, so it didn't lose its novelty.
(3) correct.
(4) It is illegal for Party C to guarantee the quality of products using its trademark. Trademark licensors must supervise the quality of products in which licensees use their registered trademarks.