20. __________ is especially popular in the speech of students, where it has yielded forms like prof for professor, phys-ed for physical education, poli-sci for political science, and burger for hamburger.
(A) Conversion
(B) Backformation
(C) Onomatopoeia
(D) Clipping

Types of Word Formation

1. Coinage創新字: Invention of totally new words; extension of a name of a product from a specific reference to a more general one
   e.g., Kleenex, Xerox, and Kodak
   ◎Eponyms: words based on a name of a person or a place.
     e.g., sandwich
2. Borrowing借字: Taking over of words from another language
3. Compounding複合: Two or more words joined together to form a new word.
   e.g., Home + work→homework (N)
4. Blending合音: Similar to compounds, but in blending only parts of the words are combined.
   e.g., motor + hotel→motel
5. Clipping簡縮: Shortening a word by deleting one or more syllables
6. Backformation反向構詞法: Creative reduction due to incorrect morphological analysis
   e.g., 先有television才有televise
7. Conversion/Functional Shift功能的轉換: Assigning an already existing word to a new syntactic category.
8. Acronyms縮略語: Words derived from the initials of several words
   e.g., United States of America → USA
9. Derivation衍生(附加詞餟): The most common word formation process; affixes 

Onomatopoeia擬聲詞

Onomatopoeia is the process of creating a word that phonetically imitates, resembles, or suggests the sound that it describes.

Common occurrences of words of the onomatopoeia process include animal noises such as "oink", "miaow" (or "meow"), "roar" and "chirp". 

Clipping簡縮＝abbreviation

ex.pro=professor

exam=examination