Question

Environmental exposures, such as house dust mites and environmental tobacco smoke, are important triggers of an attack.

Answer 1

Hi, 

The thesaurus is for looking up synonyms and antonyms of a word. 
The dictionary is for the meaning of a word.
Maybe this could help in the future. 

So the answer is A.

Hope this helps. c:

Answer 2

A thesaurus is used to find synonyms and antonyms of a word

A. Would be your answer