when did that happen
when do that happen
conj v comp v
when did that happen ?
w ɛ n WORD_BOUNDARY d ɪ d WORD_BOUNDARY ð æ t WORD_BOUNDARY h æ p ə n WORD_BOUNDARY
w h e n WORD_BOUNDARY d i d WORD_BOUNDARY t h a t WORD_BOUNDARY h a p p e n WORD_BOUNDARY