SAT Newly Defined Functions

SAT® Math Level 2

For any numbers \(m\) and \(n\), let \(m \oplus n\) be defined as \(m \oplus n= m-n+n^{2}\). Which of the following will never be negative?

I. \( a \oplus a\)
II. \((a+b) \oplus b\)
III. \((a+b) \oplus (a+b)\)