(diphthongization of mid vowels under stress), they appear normally in stressed syllables and make morphological alternations with the mid vowels and . In addition to these, the semivowels and can be combined (either before, after, or both) with most vowels. One view considers that only and can follow an obstruent-liquid cluster such as in broască ('frog') and dreagă ('to mend') and form real diphthongs, whereas the rest are merely vowel–glide sequences. The traditional view (taught in schools) considers all of the above as diphthongs. As can be seen from the examples above, the diphthongs and contrast with and respectively, though there are no minimal pairs to contrast and . Impressionistically, the two pairs sound very similar to native speakers. Because doesn't appear in the final syllable of a prosodic word, there are no monosyllabic words with ; exceptions might include voal ('veil') and doar ('only, just'), though Ioana Chițoran argues that these are best treated as containing glide-vowel sequences rather than diphthongs. In some regional pronunciations, the diphthong tends to be pronounced as a single vowel . Other triphthongs such as and occur sporadically in interjections and uncommon words. Diphthongs in borrowings Borrowings from English have enlarged the set of ascending diphthongs to also include , , , and , or have extended their previously limited use. Generally, these borrowings have retained their original spellings, but their pronunciation has been adapted to Romanian phonology. The table below gives some examples. Borrowings such as whisky and week-end are listed in some dictionaries as starting with the ascending diphthong , which corresponds to the original English pronunciation, but in others they appear with the descending diphthong . Vowel alternations Romanian has vowel alternation or apophony triggered by stress. A stressed syllable has a low vowel, or a diphthong ending in a low vowel, and an unstressed syllable has a mid vowel. Thus alternates with , with , and with . This alternation developed from Romanian vowel breaking (diphthongization) and reduction (weakening). The Eastern Romance mid vowels were broken in stressed syllables, giving the Romanian diphthongs , and the low vowel was reduced in unstressed syllables, giving the Romanian central vowel . These sound changes created the stress-triggered vowel alternations in the table below. Here stressed syllables are marked with underlining (a): This has since been morphologized and now shows up in verb conjugations and nominal inflection: oaste — oști, 'army' — 'armies'.