A radical skeptic might be willing to doubt which of the following?

3 + 5 = 8
Grass is green.
Cheese is fattening.
*All of the above
Is this correct?

Right.

http://en.wikipedia.org/wiki/Radical_skepticism

I would say all of the above.

But what do you think?

A radical skeptic is someone who is extremely skeptical and doubts almost everything. In this case, a radical skeptic might be willing to doubt all of the statements given:

- 3 + 5 = 8: A radical skeptic might question the validity of basic arithmetic and doubt that this equation is true.
- Grass is green: A radical skeptic might argue that what we perceive as green may not be the same for everyone and question the objective reality of color.
- Cheese is fattening: A radical skeptic could doubt any widely accepted claims about nutrition and question whether cheese is actually fattening.

Therefore, the correct answer is "All of the above" since a radical skeptic would be willing to doubt all three statements.