何が起こったのか説明できない。

what; how many; you-know-what; that; whatsit; what's the expression; what do you call them; what?; hey!

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to occur; to happen

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way

explanation; exposition

to be able (in a position) to do; to be up to the task; to be ready; to be completed; to be made; to be built; to be good at; to be permitted (to do); to become intimate; to take up (with somebody); to grow; to be raised; to become pregnant