B.
Because when doing the math, letter B fits the criteria of a quadratic equation. Which is ax^2 + bx + c = 0.
A is wrong because if we were to do the math, there would be no ax^2. The most important thing in a quadratic equation is the term ax^2, bx and c do not matter as much.
C is wrong because there cannot be a greater exponent than ^2.
D is wrong because of the same reason as letter a.