【正确答案】正确答案：In English, there is a rule that /p/ is unaspirated after /s/ but aspirated in other places. So /p/ in pat, tap is aspirated but unaspirated in spat since it is after /s/. To bring out the phonetic difference, an aspirated sound is transcribed with a raised "h" after the symbol of the sound. So a phonetic transcription for peak is [p ^h i: k] and that for speak is [spi: k]. So [p, p ^h ] are two different phones and are variants of the phoneme /p/. Such variants of a phoneme are called al-lophones of the same phoneme. The allophones are said to be in complementary distribution because they never occur in the same context: [ p ] occurs after [ s ] while [ p ^h ] occurs in other places. We can present this rule as: /p/→[p]/[s]________ [p ^h ] elsewhere(note: ___________is the position in which /p/ appears) In addition sometimes a phoneme may also have free variants. The final consonant of tap may not be realized by some speakers so there is no audible sound at the end of this word. Such phenomenon is called free variation.