If you have submitted a patent application for an engine in China, and then a patent application for an automobile in China B, and now you intend to submit an international patent application for C, then C can claim the priority of the patent application in China, as long as it does not exceed the priority period of 1 year.
If it does not exceed 1 year from the filing date of A, C can claim the priority of A and B at the same time, of course, only one will do.
If it has exceeded 1 year since the filing date of A, but it has not exceeded 1 year since the filing date of B, then C can only claim the priority of B. ..