21______________ is a process that inserts a syllabic or a non-syllabic segment within an existing string of segments.
(A) Metathesis
(B) Epenthesis
(C) Deletion
(D) Vowel reduction

(A) Metathesis (音位轉換)

--> The process by which two sound segments switch their position.

沒有原因(或許是利於發音)，且多發生於小朋友身上。

    (1) Example: asked /æskt/ --> /ækst/

    (2) Fish phenomenon: fish /fiʃ/ --> /fis/

(B) Epenthesis (增音、插音)

-->The process by which a sound segment is inserted into the middle of the word.

    (1) Plural morpheme (複數): boxes (/ks/)、buses、churches、buzzes、garages (/əz/)

    (2) Past tense (過去式): needed

    (3) Schwa (/ə/) is inserted between front vowel and /l/ which occurs word finally.

    --> Front vowel is retracted. (舌頭位移): seal /sil/ --> /siəl/

(C) Deletion：方便發音

    (1)  A process by which a sound segment is deleted when occurring between consonants.   

    --> grandmother、best game

   (2) Schwa tend to be deleted when occurring in an unstressed syllable

    Example: history /histərɪ/ --> /histrɪ/

(D) Vowel reduction (元音弱化)

-->Certain vowels might undergo qualitative changes in unstressed positions is likely to be familiar to anyone who has taken an introductory phonology course.

    母音變成Schwa /ə/ 

Metathesis音位轉換

The rearrangement of two consonants in a syllable.

Metathesis is responsible for some common speech errors, such as children acquiring spaghetti as pasketti. 

Examples:

«  ask /ɑsk/ → /ɑks/             (switching)

«  play /pleɪ/→/peɪl/           (transposition) (Transpose to either side of a vowel.)