First of all, make sure that the priority is claimed by the same applicant, and the 12-month priority is for invention and utility. So question 1: Priority can only be used once, that is to say, if it is requested according to situation B, C cannot ask for it. Of course, applying for B and C at the same time is a special situation. Question 2: In this case, it is possible to claim A’s priority, but if it exceeds the protection scope of A’s priority, it will not enjoy priority, and there is no basis for citation. That is to say, as long as there is no impact on the three genders between the two applications, B and C can pass. If you are unlucky, you can only modify it to the protection scope of A.