Classification of the main allophones in english language
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resources; https://www.britannica.com/topic/allophone
"A Course in English Phonetics for Spanish speakers"D. Finch/ Ortiz Lira
one of the phonetically distinct variants of a phoneme.
The occurrence of one allophone rather than
another is usually determined by its position
in the word (initial, final, medial, etc.) or by its
phonetic environment.