Network cluster behavior refers to a certain number of relatively unorganized netizens, in a network environment or under the influence of network transmission, for a group of behaviors that are jointly affected or stimulated. According to the above definitions, which of the following is behaviors of network clusters? ['"69" Jihad launched by netizens to resist irrational star chasing.', 'In order to investigate the "Chen Yi sells himself to save his mother" incident that was popular on the Internet, a Shenzhen netizen went to Sichuan to investigate the truth.', 'A university requires students to scan QR codes through classroom WeChat to complete sign-in work.', 'Guild members meet irregularly offline in the "World of Warcraft" game developed by Blizzard.']