What form should I use to apply a tourist visa. I am a American Citizen & holding US Passport?

You should fill Form V.2011A, you don't need to fill Form 2011B.

If you are applying to work or study in China, or if someone else travelling with you shares the same passport, or if you are applying for a visa in a country or territory other than the country of your current nationality, you should fill out the Supplementary Visa Application Form (Form V.2011B)