21. ______ is a process by which a word of wider meaning acquires a specialized sense. For example，the original meaning of the word“meat” was food and the modern meaning is edible flesh. (      )

A. Conversion                                               B. Elevating

C. Narrowing                                                D. Formation

22. Which of the following is NOT a context clue? (      )

A. Relevant details.                                        B. Sentence structure.

C. Synonymy.                                                D. Antonymy.

23. The sentence “I like Mary better than John’’ is ambiguous due to ______. (      )

A. grammatical context                                   B. polysemy

C. antonymy                                                  D. hyponymy

24. In the sentence“Copernicus believed in a heliocentric universe，rather than in the geocentric theory”，the meaning of heliocentric call be inferred from the clue of ______.(      )

A. relevant details                                          B. word structure

C. antonymy                                                  D. hyponymy

25. “Tooth and nail” is all idiom ______ in nature. (      )

A. verbal                                                       B. nominal

C. adjectival                                                  D. adverbial