You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Dutch_language

Context:
Unique to the development of Dutch is the collaps of older ol/ul/al + dental into ol + dental, followed by vocalisation of pre-consonantal /l/ and after a short vowel, creating the diphthong /ɑu/ e.g., Dutch goud, zout and bout corresponds with Low German Gold, Solt, Bolt; German Gold, Salz, Balt and English gold, salt, bold. This is the most common diphthong along with /ɛi œy/. All three are commonly the only ones considered unique phonemes in Dutch. The tendency for native English speakers is to pronounce Dutch names with /ɛi/ (written as ij or ei) as /aɪ/, (like the English vowel y) which does not normally lead to confusion among native listeners, since in a number of dialects (e.g. in Amsterdam) the same pronunciation is heard.

Question:
What's the term we use for the type of sound made for two vowels in words like the Dutch "goud" or "zout"?

diphthong