Get ABC = ab (-a-b) =-ab (a+b) =-a 2 * b-a * b 2 = 4.

B * A 2+B 2 * A+4 = 0。

Because a, b and c are real numbers.

So the discriminant = b 4-4 * b * 4 = b 4- 16b > =0.

At this time, let b be the largest number among a, b and c, and b >；; 0

Get b 3- 16 > =0.

b^3>； = 16

B>= number of cubic roots16 > 2.5

Therefore, the value of at least one of A, B and C is greater than 2.5.