Non-cause management: refers to the management of other people's affairs without legal obligations. Which of the following acts is causeless management? ["Xiao Hong's stamps collected by her parents after she left for college.", 'Han Jian is traveling and her aunt Wang helps her to repair her house.', 'Wang Xin took his nephew to swim, the nephew fell into the water and called for help, and Wang Xin rescued him.', 'The downstairs of a resident is blocked, and the property management office sends someone to clear it.']