A:	because they don't, they don't degrade over such a period of time.
ʌ WORD_BOUNDARY b ɪ k ʌ z WORD_BOUNDARY ð eɪ WORD_BOUNDARY d oʊ n t WORD_BOUNDARY ð eɪ WORD_BOUNDARY d oʊ n t WORD_BOUNDARY d ɪ ɡ ɹ eɪ d WORD_BOUNDARY oʊ v ə ɹ WORD_BOUNDARY s ʌ t̠ʃ WORD_BOUNDARY ʌ WORD_BOUNDARY p iə ɹ ɪ ə d WORD_BOUNDARY ʌ v WORD_BOUNDARY t aɪ m WORD_BOUNDARY