Hello, I have A question is how to set up A special logic task: I created A, B, C three tasks, and connected, how should I do to achieve the start to do A task and will only display A task, when I finish A task, the task will show B, B task displays C task again, thank you for your help ：）

Please check the wiki before asking next time ;). Here is a page explaining the visibility of quests and how to configure them. For your purposes, it sounds like you should just link them and set all quests to "UNLOCKED" (or the first to unlocked and the ones after to "chain"). This will make the quest only show if it is currently able to be worked on (meaning all prerequisites are finished already). "NORMAL" is basically the same, except it shows what quests will be unlocked on completion of the current one.