What does Lexicology, a brunch of linguistics study?

What do we understand by etymological doublets?

1. 
   Doublets are the words with the same source but different in phonemic shape.
   
2. 
   These are words which have the same meaning but differ in phonemic shape
   
3. 
   *These are words which originated from the same source, but differ in phonemic shape and in meaning.
   
4. 
   Such words which are the same in phonemic shape but differ in meaning.
   
5. 
   Doublets are words which have the same phonemic shape and meaning.
   

16. 
    There are three types of synonyms: ideographic, stylistic and absolute. What is a stylistic type?
    

1. 
   It differs in shades of meaning.
   
2. 
   *lt differs in stylistic characteristics.
   
3. 
   It coincides in all their shades of meaning.
   
4. 
   It has the same concept but differs in meaning.
   
5. 
   It has the same stylistic characteristics.
   

16. 
    Can we define the language spoken in the USA as an American language?
    

1. 
   We define it as an American language.
   
2. 
   We define it as one of the dialects of the English language.
   
3. 
   We define it as an independent language.
   
4. 
   We define it as a different kind of the English language.
   
5. 
   *We define it as a regional variety of the English language.
   

16. 
    To which parts of speech do most antonyms belong?
    

1. 
   They mostly belong to verbs.
   
2. 
   They mostly belong to nouns.
   
3. 
   They mostly belong to adverbs.
   
4. 
   *They mostly belong to adjectives.
   
5. 
   They mostly belong to verbs and nouns.
   

16.