光在哪，神在那。

CThe morpheme used to express indefiniteness in English has two forms-a before a word that begins with a consonant and an before a word that begins with a vowel. The variant forms of a morpheme are called its .
(A) free morphemes
(B) bound morphemes
(C) allomorphs
(D) affixes

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(A) free morphemes 自由詞素 (可以自己單獨存在且有意義的)

Morphemes that can stand alone to function as words are called free morphemes. 

They comprise simple words (i.e. words made up of one free morpheme) and compound words (i.e. words made up of two free morphemes).

【舉例】

Simple words : the, run, on, well

Compound words : keyboard, greenhouse, bloodshed, smartphone

(B) bound morphemes 限制詞素/結合語素（不能自己存在，一定要跟別人合在一起）

Morphemes that can only be attached to another part of a word (cannot stand alone) are called bound morphemes. 

【舉例】（就像我們常用的字根字首！）

pre-, dis-, in-, un-, -ful, -able, -ment, -ly, -ise

pretest, discontent, intolerable, receive

(C) allomorphs同位異形

A morpheme is indicated as one or more morphs (surface forms) in different environments. These morphs are called allomorphs.

(D) affixes 詞綴

a group of letters added to the beginning or end of a word to change its meaning

【function】affix : prefix(字首)+root(字根)+suffix(字尾)

【meaning】word: free morphemes + bound morphemes

CWhich statement best describes prepositions, such as at, for, and by?
(A) Content and free morphemes
(B) Content and bound morphemes
(C) Function and free morphemes
(D) Function and bound morphemes 

BWhich of the following exemplifies phonologically-conditioned allomorphic alternation?
(A) The variants of /t/ as in tie, stay, smart
(B) The variants of /d/ as in walked, played, started
(C) The variants of the lateral sound as in light and tell
(D) The alternation between /f/ and /v/ as in wife–wives, leaf–leaves

小試身手（紅色free morphemes ; 藍色bound morphemes）

(1) encountered = en + counter + ed

(2) assignment = assign + ment

參考網址:

https://pediaa.com/what-is-the-difference-between-allophone-and-allomorph/