Formal Writing: forbidden words

Hi everyone,

We all know that formal writing is more strict than casual writing. Some  

vocabulary that is accepted in regular speech, have no room in formal writing. So take a look at this list and make sure you are not making any of these
1. Alot
2. Let's
3. Gonna
4. Wanna
5. Ain't
6. Could of
7. And etc.
8. Furthest
9. Its'
10. Cause (meaning because)