要參加jupas的話，高考要報多少科？

you may do so, but some uni do not accept combine cert., like CUHK (that is what I have heard).
so if you really wanna get into uni with more choices, you better take at least 2.5 subs, i.e. 2ALs and 1AS
in fact, i know there are ppl only take 2AL or 1AL and 2AS, but i don't think that is good choice, as most uni in HK have to count 2.5subs for reference........... if u only take 2 subs, which u will lose marks in advance.