english: Scientists are still investigating  potential triggers for the three types of primary headaches: recurring, long-lasting migraines; intensely painful,  rapid-fire cluster headaches; and, most common of all,  the tension headache.
non_english: Naučnici i dalje ispituju potencijalne uzročnike u tri tipa primarnih glavobolja: ponavljajuće, dugotrajne migrene, izuzetno bolne, nagle klaster glavobolje i, najčešće od svih, tenzione glavobolje.