Why t'as ? it is tu as. I do know how to conjugate avoir Is this new ?
Really if on the streets of Paris the rules changed should we not know the rules ? Do they say for example do they say "il y a" on the streets ?
Every language has its informal shortenings. tu very commonly elides to t' before a vowel regardless of the word that follows (verb or pronoun), but it is considered nonstandard so it's not accepted on Duolingo. A comparable thing commonly happens to "il y a": the il is very often dropped, leaving only "ya" (and y'avait, y'aura, y'a eu etc.) The y and verb are usually written without a space inbetween to reflect that they're pronounced as one.