does all information of wikipeadia true?

Absolutely not .You need to check yourself .If you really don't know whether it is true or not ,you can discuss with others ,teachers ,experts or friends.

dont listin to what your teachers say, if there work is cited then it is probably true

Yeah sure is, and it updates some general information regularly.... And what kind of information you have in doubt in wikipeadia?.... Usually an information in doubts or lack of information are in some personal or private company information....

Most of the information in Wikipedia is true. just check out for the Wikipedia comments. if it says "this article requires citation and verification" or " this article does not site any reference or source" it means the article is yet to be verified and may be prone to errors. otherwise it is true. but still it is advisable to do cross reference.