A is a tool used for classifying and categorizing.

Ask.com can be considered a search engine.As a search engine, it is a software you would use in order to search for information, as the name itself says. You want to find out something, and then you go to Ask.com in order to find that particular piece of information, which is the purpose of search engines, such as Google, Bing, Yahoo!, or Ask.com.

Explanation:

hope this helps

hm, switch the relative; nominative and indefinite; objective ? not too bright in the knowledge of the english.

i think it is b. hope this !