An abstract linguistic unit which is realized in speech in the material form of its variants is called

• a phoneme 

• an allophone

• a syllable

• an utterance

Phonetically similar sounds that do no contrast with each other are

• phonemes

• allophones

• syllables

• utterances

The opposition /p/ versus /f/ like in PAIR-FAIR is called

• a PHONOLOGICAL OPPOSITION

• a ZERO OPPOSITION

• a minimal pair

• a  minimal set

The opposition /p/ versus /-/ like in PAIR-AIR is called

• a PHONOLOGICAL OPPOSITION

• a ZERO OPPOSITION

• a minimal pair

• a minimal set

The pair of words which differ in only one speech sound is called

• a  PHONOLOGICAL OPPOSITION

• a ZERO OPPOSITION

• a minimal pair

• a minimal set

Two different realizations of the phoneme can be substituted by each other without changing the meaning, e.g. /b/ in BAD can be pronounced with no voicing or with full voicing. It’s called

• a PHONOLOGICAL OPPOSITION

• free variation

• a minimal set

• complementary distribution

When allophones never occur in identical positions, they are

• a PHONOLOGICAL OPPOSITION

• free variation

• a minimal set

• complementary distribution

IDIOLECTAL variations

• are caused by historical tendencies in certain localities

• are caused by the phonetic positions and phonetic environment

• embrace the individual peculiarities of articulating sounds caused by the shape of the speaker’s speech organs and by his articulatory habits

• are caused by the speaker’s educational background

DIAPHONIC variations

• are caused by historical tendencies in certain localities

• are caused by the phonetic positions and phonetic environment

• embrace the individual peculiarities of articulating sounds caused by the shape of the speaker’s speech organs and by his articulatory habits

• are caused by the speaker’s educational background

ALLOPHONIC variations

• are caused by historical tendencies in certain localities

• are caused by the phonetic positions and phonetic environment

• embrace the individual peculiarities of articulating sounds caused by the shape of the speaker’s speech organs and by his articulatory habits

• are caused by the speaker’s educational background