1. Our biology professor says handwashing is important to prevent the spread of germs. I'm not taking her advice though, heard she used to be an alcoholic . Which fallacy?

The fallacy is that you won't believe your biology teacher because she used to be an alcoholic over a commonly known fact. People can change, and this is proven by the fact that the word "used" is in the sentence. "Heard" is seen as well, meaning that you don't know for sure. Besides that, it is widely known that you should wash your hands to prevent the spreading of germs.

op: object of preposition

b is the answer